Software Licensing Glossary, Key Terms

Copyleft: A licensing approach requiring derivative works to be distributed under the same license terms. The GPL family uses copyleft to ensure code stays open.

Permissive License: A license allowing use, modification, and distribution with minimal restrictions, including in proprietary software. MIT and BSD are canonical examples.

Proprietary License: A license restricting use, modification, or distribution. Source code is typically not made available.

Dual Licensing: Offering the same software under two different licenses, typically one open-source and one commercial.

GPL (GNU General Public License): A strong copyleft license. Any distributed work incorporating GPL code must itself be GPL-licensed. Version 3 addresses patents and tivoization.

LGPL (Lesser GPL): A weaker copyleft license allowing linking from proprietary software while requiring modifications to the library itself to stay open.

MIT License: A minimal permissive license requiring only that the copyright notice and license text be preserved.

Apache License 2.0: A permissive license with an explicit patent grant and trademark restrictions.

BSD Licenses: A family of permissive licenses (2-clause and 3-clause variants) similar in spirit to MIT, originating from Berkeley Unix.

MPL (Mozilla Public License): A file-level copyleft license, modifications to licensed files stay open, but new files can be proprietary.

Tivoization: Distributing GPL software on hardware that refuses to run modified versions, addressed by GPLv3’s anti-tivoization clause.

License Compatibility: Whether code under two different licenses can legally be combined. Permissive licenses are generally compatible with copyleft ones, not vice versa.

Contributor License Agreement (CLA): A legal agreement contributors sign granting the project maintainer rights to relicense their contributions.

SPDX Identifier: A standardised short string identifying a license (e.g., MIT, Apache-2.0, GPL-3.0-only), used in package metadata.

Return to the Licensing Hub for license comparisons, or explore Tools for license-scanning utilities.

Strong Copyleft: Derivatives of the whole work must adopt the same license. GPL-2.0-only and GPL-3.0-only are the canonical examples.

Weak Copyleft: Copyleft applies only to the licensed component itself, not to works that link against it. LGPL and MPL are weak/medium copyleft.

Network Copyleft: Triggers copyleft obligations when the software is offered over a network, not just distributed. AGPL-3.0 closes the “hosting loophole” that allowed SaaS providers to modify GPL software without sharing changes.

Share-Alike: The Creative Commons term (SA) for the copyleft principle: adaptations must be licensed under the same terms.

Patent Grant: An explicit licence to use patents held by contributors that read on the software. Apache-2.0 grants it expressly; GPLv3 includes it indirectly; MIT/BSD rely on implied licence only.

Attribution Clause: The requirement to preserve copyright notices and license text in copies. Present in every OSI-approved permissive license.

Notices File: A compiled listing of all dependencies and their licenses, required for compliance when shipping permissively-licensed code in proprietary products.

License Proliferation: The historical over-creation of slightly-different open-source licenses, raising compatibility analysis costs. The SPDX list now tracks 600+ identifiers.

Public Domain Equivalent: Licenses/declarations that surrender copyright entirely: CC0 and the Unlicense. Not recognised in all jurisdictions (notably Germany), which is why most projects still prefer a formal license.

Non-Commercial Clauses: Restrictions on commercial use that fail the Open Source Definition (freedom to use for any purpose). CC BY-NC is common but not open source.

Copyleft Compliance Checklist: Distributing GPL code requires: preserving notices, providing the corresponding source (or written offer), stating changes, and passing the license terms downstream.

Vulnerability vs License Scanning: SCA (Software Composition Analysis) tools audit both security advisories and license obligations across dependency trees.

License Header: A short declaration at the top of each source file; SPDX recommends a single-line // SPDX-License-Identifier: <id> rather than full license text.

See the Licensing Hub for per-license comparison tables and the Tools section for scanners that automate compliance checks.

BSL (Boost Software License): A permissive license similar to MIT with an explicit patent grant and no attribution requirement in binaries.

Zlib License: A short permissive license requiring altered source versions to be plainly marked.

Artistic License 2.0: A Perl’s-license allowing redistribution with modified source under conditions; OSI-approved but rarely chosen today.

EPL (Eclipse Public License): A weak-copyleft license (EPL-2.0 current) used by Eclipse, Jetty, and enterprise Java tooling; module-level copyleft.

CDDL (Common Development and Distribution License): File-level copyleft license originated by Sun for OpenSolaris; compatible with GPL under certain interpretations.

SSPL (Server Side Public License): MongoDB’s license requiring source disclosure for offering the software as a service; rejected by OSI as not open source.

BSL (Business Source License): Time-delayed open source, code converts to an open license after a change date (MariaDB, HashiCorp post-2023).

AGPL (Affero GPL): GPLv3 plus network-use clause; the standard choice for server software that wants to force SaaS disclosure.

CC BY: Creative Commons attribution license for creative works; permissive but not recommended for software (no patent or source provisions).

MIT-0: MIT variant with the attribution condition removed, effectively a public-domain dedication with warranty language.

Derivative Work: Copyright law’s term for adaptations; the trigger point for copyleft obligations and the reason linking analysis matters.

Mere Aggregation: Distributing independent programs side-by-side (e.g., on one disk image) without combining them into a single work; GPL obligations do not cross this boundary.

Static vs Dynamic Linking: The legal debate over whether linking produces a derivative work; the FSF says yes for both, most practitioners treat dynamic linking as a weaker claim.

Operating System Modification Exception: GPLv3 language covering system libraries and kernel modules whose linking the OS itself permits.

Conveying vs Mere Distribution: GPLv3’s broader term covering both physical transfer and network distribution of object code.

Installation Information: GPLv3’s requirement to provide build/install instructions when conveying object code for consumer devices.

Termination and Cure: GPLv3’s provision allowing licensees who violate terms to regain the license automatically if they cure within 30 days, a first-offence forgiveness clause.

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