Glossary¶

Key terms used throughout this guide. Terms marked with * appear as tooltips on highlighted text throughout the site.

A¶

Attribution*¶

Credit given to the original creator as required by a license. Almost every open source license requires attribution when redistributing code.

AGPL (Affero General Public License)¶

A strong copyleft license that extends GPL to cover network use. If you run modified AGPL software as a web service, you must provide source code to users.

B¶

Binary*¶

Compiled, machine-readable form of software, as opposed to source code. Many licenses have different requirements for source vs binary distribution.

BSD License¶

A family of permissive licenses from UC Berkeley. The 2-clause and 3-clause versions are most common today.

C¶

Contributor*¶

Someone who adds code or content to a project. Contributors may grant licenses to their contributions.

Contributor License Agreement (CLA)¶

A legal agreement where contributors grant additional rights to a project. Often used to enable dual licensing or relicensing.

Copyleft*¶

A licensing approach requiring derivative works to use the same license. Ensures that modifications remain open source.

Copyright¶

Legal right automatically granted to creators of original works. In most jurisdictions, this is automatic upon creation.

D¶

Derivative Work*¶

A new work based on or derived from an existing copyrighted work. Whether something is a derivative work is often the key question for copyleft licenses.

Disclaimer*¶

Statement limiting liability, typically required to be preserved when redistributing software.

Distribution*¶

The act of sharing or providing software to others. Most license obligations are triggered by distribution.

Downstream*¶

Projects or users that build upon or use an upstream project. In open source, changes flow from upstream to downstream.

Dual Licensing*¶

Offering software under two different licenses simultaneously. Common for commercial open source: GPL for community, paid license for proprietary use.

F¶

FLOSS*¶

Free/Libre and Open Source Software. Emphasizes the freedom aspect of "free."

FOSS*¶

Free and Open Source Software. General term for software with open source licenses.

Free Culture¶

Works licensed to allow sharing, modification, and commercial use. CC BY, CC BY-SA, and CC0 are Free Culture licenses; NC and ND variants are not.

Free Software¶

Software that respects users' freedom. Defined by the FSF as having four freedoms: to run, study, redistribute, and modify.

FSF*¶

Free Software Foundation. Organization that advocates for free software and maintains the GPL.

G¶

GPL (General Public License)¶

The most important copyleft license, created by the FSF. Requires derivative works to be GPL-licensed when distributed.

Gratis*¶

Free as in cost—referring to price, not rights. Software can be gratis without being libre.

L¶

LGPL (Lesser General Public License)¶

A weak copyleft license for libraries. Allows proprietary software to link against LGPL libraries while requiring library modifications to be shared.

Libre*¶

Free as in freedom—referring to rights and permissions, not price. The "free" in "free software."

License Compatibility*¶

Whether code under different licenses can be legally combined. Not all open source licenses are compatible with each other.

M¶

MIT License¶

The most popular permissive open source license. Extremely short and simple, requiring only attribution.

Moral Rights¶

Rights to attribution and integrity that exist in some legal systems. Some cannot be waived even with permissive licenses.

MPL (Mozilla Public License)¶

A weak copyleft license operating at the file level. Modified files must be MPL; new files can use any license.

N¶

NonCommercial*¶

License restriction prohibiting use for commercial purposes. Used in CC BY-NC and related licenses.

NoDerivatives*¶

License restriction prohibiting creation of derivative works. Used in CC BY-ND and related licenses.

Notice*¶

Required text that must be included when redistributing licensed software. Usually includes copyright notice and license reference.

O¶

Open Source¶

Software with a license approved by the OSI meeting the Open Source Definition. Source code is available and users have specific guaranteed rights.

Open Source Definition¶

Criteria established by the OSI for what makes a license "open source." Includes free redistribution, source availability, and no discrimination.

OSI*¶

Open Source Initiative. Organization that reviews and approves licenses as "open source."

OSI-Approved*¶

A license officially recognized by the Open Source Initiative as meeting the Open Source Definition.

P¶

Patent Grant*¶

License provision giving users rights to any patents held by contributors. Included in Apache 2.0, GPL v3, and MPL 2.0.

Permissive License*¶

A license that allows use with minimal restrictions, including in proprietary software. Examples: MIT, BSD, Apache 2.0.

Proprietary*¶

Software with restricted rights, typically closed-source and commercially licensed.

Public Domain*¶

Works not protected by copyright, free for any use without restriction. In some jurisdictions, creators cannot directly dedicate to public domain.

S¶

License term requiring derivatives to use the same or compatible license. The "SA" in CC BY-SA.

ShareAlike¶

See Share-Alike.

Source Available¶

Software whose source code is visible but which has restrictions incompatible with open source. SSPL and BSL are source available, not open source.

Source Code*¶

Human-readable form of software, as opposed to compiled binary code. Many licenses require source availability.

SPDX*¶

Software Package Data Exchange. Standard format for communicating license information. Provides standardized identifiers like MIT or Apache-2.0.

Strong Copyleft*¶

Copyleft that applies to the entire combined work, not just modified files. GPL is strong copyleft.

Sublicense*¶

The right to grant license rights to others. Permissive licenses generally allow sublicensing.

Using hardware restrictions to prevent users from running modified software, even when the source code is available. Named after TiVo devices that ran GPL-licensed Linux but used cryptographic signatures to block user modifications. GPL v3 specifically prohibits this practice.

U¶

Upstream*¶

The original project from which a fork or derivative is created. Changes often flow from upstream to downstream projects.

V¶

Viral License*¶

Informal term for copyleft licenses that "spread" to derivative works. Generally considered pejorative.

W¶

Weak Copyleft*¶

Copyleft that only applies to modifications of the original files, not the larger work. LGPL and MPL are weak copyleft.