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Glossary Open Source

Glossary Open Source

All technical terms of the article The History of Open Source in alphabetical order. The number at the end names the section that introduces the term.

A

  • AGPL – Affero General Public License: a version of the GPL that extends copyleft to programs that are only operated as a service on the net; since 2024 the licence of Elasticsearch, since 2025 of Redis. 7
  • Android – Operating system for phones with Linux as kernel and an interface under the Apache licence, announced in 2007, released in 2008; runs on a good seven out of ten smartphones. 6
  • Apache – Web server, created in 1995 from patches for the NCSA server, the most used from 1996; the Apache Software Foundation (1999) became the model for all foundations. 4
  • Apache licence – Permissive licence of the Apache Software Foundation; version 2.0 (2004) was the first widespread licence to contain an explicit patent grant by the contributors. 5

B

  • Bazaar – Raymond’s image for the development of Linux: many contributors, early and frequent releases, users as co-developers; the counter-image to the cathedral. 4
  • Berkeley Software Distribution (BSD) – Unix variant of the University of California, compiled from 1977 by Bill Joy; brought TCP/IP and the sockets in 1983; free from 1994 after the lawsuit with AT&T (FreeBSD, NetBSD, OpenBSD). 2
  • Bermuda Principles – Agreement of the Human Genome Project of 1996 to release decoded sequences within 24 hours; made open data the norm of biology. 6
  • BSD licence – Permissive licence from Berkeley (1990) that permits everything as long as the copyright notice remains; the obligation to mention in advertising was struck in 1999. 3
  • Business Source License (BSL) – Source-available licence that prohibits competing with the maker and releases the code after some years; chosen by HashiCorp for Terraform in 2023. 7

C

  • Cathedral – Raymond’s image for development by a closed team that releases rarely and after long checking. 4
  • Cloud – Renting out of computing power and services over the net, since 2006 (Amazon); runs on Linux and open tools, but as a service passes on no code. 6
  • Compiler – Program that translates source code into machine code. 1
  • Container – Packaging of a program with everything it needs so that it starts the same everywhere; Docker (2013) and Kubernetes (2014). 6
  • Contributor License Agreement (CLA) – Agreement by which a contributor grants a company or foundation the right to use their code under any licence; the precondition of the licence changes of 2018 to 2024. The Linux kernel instead requires only the Developer Certificate of Origin. 7
  • Copyleft – Stallman’s device: copyright is used to require that changed and redistributed versions stay under the same licence and with source code; realised in the GPL. 3
  • Copyright – Right of the creator of a work to decide about its reproduction; explicit for programs since 1980 (USA) and 1985 (Germany); the foundation of every licence. 1
  • Creative Commons – Licences of 2002 for texts, images and music modelled on free software licences, in gradations. 6
  • Crypto wars – Dispute of the 1990s over the export of strong encryption from the USA; ended in 1999 with source code classed as protected speech and in 2000 with the release of published code. 8
  • Cyber Resilience Act – EU regulation of 2024 that makes manufacturers of networked products liable for their security, with obligations from 2027; exempts non-commercial open-source development. 7

D

  • Debian – Distribution founded in 1993 by Ian Murdock that persists as a community project without a company; its social contract and the Debian Free Software Guidelines (1997) became the template of the Open Source Definition. 4
  • Dependency – Outside package that a program includes at build time or at run time; dependencies bring their own with them and form the supply chain. 7
  • Digital sovereignty – The ability of a state or organisation to understand, change and operate its own infrastructure without depending on a manufacturer; since the 2020s the reason given for open source in public bodies. 8
  • Distributed version control – Version control in which every participant holds the complete history of the project and works without a central server; Git. 6
  • Distribution – Compilation of Linux kernel, GNU tools, applications and installation program that yields a usable operating system; for instance Debian, Slackware, SUSE, Red Hat. 4
  • Dual licensing – Business model in which a program is offered free of charge under the GPL and for money under another licence; for instance MySQL and Qt. 5

E

  • European Union Public Licence (EUPL) – Licence of the European Commission (2007) with weak copyleft, equally binding in all official languages, for software of public administrations. 7

F

  • Fork – Splitting off of a project’s source code into a new one under a new name, which every open-source licence permits; on GitHub also the own copy for a pull request. 6
  • Foundation – Neutral carrier of a project that holds name and trademark and regulates participation; Apache, Eclipse, Linux Foundation, Cloud Native Computing Foundation. 6
  • Four freedoms – The FSF’s definition of free software: to run a program for any purpose, to study and change its source code, to pass on copies, to publish changed versions. 3
  • Free software – Software that grants the four freedoms; the older name for the same thing as open source, with the freedom of the user as the reason. 3
  • Free Software Foundation (FSF) – Foundation founded by Stallman in 1985 that carries GNU, issues the GPL and maintains the definition of free software. 3

G

  • GCC – GNU C Compiler, released in 1987; the compiler with which industry accepted free software long before it shared the reasoning. 3
  • Git – Distributed version control system that Torvalds wrote for the Linux kernel in April 2005; today the tool of almost all programmers. 6
  • GitHub – Service of 2008 that hosts Git projects and introduced the pull request; more than 180 million accounts, owned by Microsoft since 2018. 6
  • GNU – “GNU’s Not Unix”: the free operating system compatible with Unix that Stallman announced in 1983; supplied compiler, editor, shell and tools, but no finished kernel. 3
  • GNU General Public License (GPL) – Copyleft licence of the FSF: version 1 of 1989, version 2 of 1991 (the licence of the Linux kernel), version 3 of 2007. 3

H

  • Hacker – Programmer who wants to understand a system down to its last corner; at MIT in the 1960s and 1970s a culture of sharing, only later also a word for intruders. 2
  • Heartbleed – Bug in OpenSSL, known since 7 April 2014, that allowed server memory to be read out; made visible that the infrastructure of the net is maintained by a few unpaid people. 6

I

  • Incompatibility – Two licences are incompatible if code under both may not be combined into one program; for instance GPL 2 and CDDL, which is why ZFS may not enter the Linux kernel. 5

K

  • KDE – Graphical working environment for Linux, begun in 1996 by Matthias Ettrich; the dispute over the licence of the library Qt led to GNOME and in 2000 to the release of Qt. 4
  • Kernel – Part of an operating system that manages processor, memory and devices and allocates them to the programs; GNU lacked one, Linux supplied it. 3
  • Kernel Enforcement Statement – Declaration by the Linux developers of 2017 to pursue licence violations first with a period to cure; the answer to enforcement that was about money. 7

L

  • LAMP – Acronym coined by c’t (1998) for Linux, Apache, MySQL and PHP, the free kit for services on the web. 4
  • LGPL – Lesser (originally Library) General Public License of the FSF (1991): weak copyleft for libraries that may also be linked into unfree programs. 3
  • Licence – Permission to use a program under conditions set by the rights holder; with closed software it restricts, with open source it permits. 1
  • Linus’s law – Raymond’s formula “given enough eyeballs, all bugs are shallow”: with enough reviewers every bug is quickly found. 4
  • Linux – Operating system kernel that Linus Torvalds began in 1991 and put under the GPL in 1992; with the GNU tools the free system that today carries servers, phones and supercomputers; version 7.0 in April 2026. 4
  • Linux Foundation – Foundation that emerged in 2007 from the Open Source Development Labs; protects the name Linux, pays Torvalds and carries projects with contributions from industry. 5
  • Log4Shell – Hole in the Java library Log4j, known since 10 December 2021, that allowed foreign code to be executed with a single line of text; an object lesson about the supply chain. 7

M

  • Machine code – The sequence of instructions that the processor executes; translated from the source code, hardly readable by people. 1
  • Maintainer – Person responsible for a subarea of a project who checks and merges patches; in the Linux kernel since the 1990s the hierarchy under Torvalds. 4
  • Minix – Small Unix-like teaching system by Andrew Tanenbaum (1987) whose source code was printed in the textbook; model and impetus for Linux. 3
  • MIT licence – The shortest and most used permissive licence, created in the mid-1980s at MIT for the X Window System. 3
  • Mozilla Public License (MPL) – Licence with weak copyleft per file, written for Mozilla in 1998, compatible with the GPL since version 2.0 (2012); the licence of Firefox and LibreOffice. 5

O

  • Open source – Software whose source code lies open and which anyone may use, read, change and pass on; name of 1998, definition by the OSI with ten criteria. 5
  • Open Source Definition – Ten criteria of the OSI (1998, from the Debian guidelines) that a licence must meet: free redistribution, source code, derived works, no exclusion of persons or purposes. 5
  • Open Source Initiative (OSI) – Organisation founded in 1998 by Perens and Raymond that maintains the term and examines licences. 5
  • Open Source Intelligence (OSINT) – Evaluation of publicly accessible sources by intelligence services; shares only the word with open-source software. 8
  • Open-source steward – Role in the Cyber Resilience Act: an organisation that looks after open-source projects and bears lighter duties for it than a manufacturer. 7

P

  • Package management – Distribution of programs as packages with a statement of their dependencies and a tool for installing and updating; dpkg, RPM, later npm and pip. 4
  • Patch – List of changed lines with which a change is sent to a maintainer; the form of collaboration by email. 4
  • Permissive licence – Licence that permits everything, including incorporation into closed products, usually only with the obligation to keep the copyright notice; MIT, BSD, Apache. 3
  • Public domain – Renunciation of all rights in a work, as with SQLite; CC0 (2009) is the declaration for it. 5
  • Pull request – Request to the maintainer to take over a change from a fork, with public discussion; introduced by GitHub in 2008. 6

R

  • Research software engineer – Profession, so named since 2012, that builds and maintains software for research so that it stays verifiable and outlives the paper. 6

S

  • SELinux – Permission model developed by the NSA, released under the GPL in December 2000, in the Linux kernel since 2003; gives every process only the rights a rule assigns to it and works solely on the local machine. 8
  • SHARE – Association of users of IBM computers founded in 1955 that exchanged programs with source code; the first form of collaboration on software. 1
  • Sockets – Interface of 4.2BSD (1983) through which programs open network connections; in every operating system to this day. 2
  • Software bill of materials (SBOM) – Parts list of all components of a program, required in the USA from government suppliers since 2021. 7
  • Software patent – Patent on an idea rather than on a particular source code; the EU directive on it was rejected by Parliament in 2005. 5
  • Source available – Model in which the source code can be read but the licence excludes users or purposes (SSPL, BSL); not open source by the OSI’s definition. 7
  • Source code – Version of a program that people write and read, in a programming language; the basis of every change. 1
  • Sovereign Tech Fund – German federal funding since 2022 for the maintenance of basic components that everyone uses and nobody pays for; since 2024 the Sovereign Tech Agency. 7
  • SPDX – Short codes of the Linux Foundation (since 2010) for licences, such as “GPL-2.0-only”, with which source files and bills of materials name the licence in machine-readable form. 7
  • SSPL – Server Side Public License of MongoDB (2018): requires everyone who offers the program as a service to open the entire service; not recognised by the OSI as open source. 7
  • Supply chain – The chain of dependencies from which a program is assembled; vulnerable to bugs, sabotage or backdoors deep in the tree (left-pad, Log4Shell, xz). 7
  • Support – Business model in which not the program is sold but tested versions, updates and help by subscription; Red Hat since 2002. 5
  • Sustainability – The question whether the maintenance of open software, on which everyone lives, is paid for and whether its carriers hold out; the core of the debate since Heartbleed (2014). 6

T

  • Tivoisation – Locking out of changed free software by signatures on a device, named after the video recorder TiVo; prohibited by GPL 3, not adopted by the Linux kernel. 6

U

  • Unbundling – IBM’s decision of 1969 to charge for software separately from the hardware; made software a commodity. 1
  • Unix – Operating system of Bell Labs (1969) that went to universities with source code because of an antitrust settlement and founded the culture of sharing; after 1984 a product of AT&T. 2

W

  • Weak copyleft – Copyleft that applies only to the library or the single file and permits incorporation into unfree programs; LGPL, MPL, EPL, CDDL. 5

X

  • X Window System – Foundation of graphical interfaces on Unix, created in the mid-1980s at MIT; origin of the MIT licence. 3
  • xz – Compression tool into which an unknown person built a backdoor from 2022 to 2024, discovered on 29 March 2024; an object lesson about trust in the supply chain. 7
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