> /v1/glossary
Open source glossary
Plain-English definitions for the licenses and concepts you actually need to understand — BSL, SSPL, AGPL, copyleft, fair-source, and more.
// LICENSES
// /glossary/agpl
GNU Affero General Public License(AGPL)
The strongest copyleft license — anyone running modified AGPL code as a network service must release their source code.
// /glossary/gpl
GNU General Public License(GPL)
The original copyleft license. Derivative works must remain GPL — the basis of free software.
// /glossary/mit
MIT License
The most permissive open source license. Use the code for anything as long as you preserve the copyright notice.
// /glossary/apache
Apache License 2.0
Permissive open source license with explicit patent grant. Used by Kubernetes, Apache projects, Android.
// LICENSE MODELS
// /glossary/bsl
Business Source License(BSL)
A source-available license that converts to an open source license after a delay (typically 4 years). Used by HashiCorp, Sentry, and others.
// /glossary/sspl
Server Side Public License(SSPL)
A copyleft license invented by MongoDB that requires anyone offering the software as a service to open source their entire stack.
// /glossary/source-available
Source-Available
Software whose source is published but whose license imposes restrictions that prevent it from being open source.
// /glossary/fair-source
Fair-Source
A category of source-available licenses that auto-convert to open source after a delay — most prominently the FSL.
// /glossary/elv2
Elastic License v2(ELv2)
Elastic's source-available license that prohibits offering the software as a managed service.
// CONCEPTS
// /glossary/copyleft
Copyleft
A licensing strategy that uses copyright law to require derivative works to remain under the same open license.
// /glossary/permissive-license
Permissive License
A license category that allows derivative works to be relicensed under any terms — including proprietary.
// /glossary/open-source-definition
The Open Source Definition
The OSI's 10-point definition of what qualifies as open source software.
// /glossary/relicensing
Relicensing
Changing the license of a software project — sometimes from open source to source-available.