Open source license
Also called OSS license, open-source licence.
The terms under which open source code may be used, changed and shared, including what you owe in return.
Last updated
What it is.
Almost every product is built on open source libraries. Each comes with a licence. The Open Source Initiative keeps the Open Source Definition and a list of licences that meet it, and SPDX gives each common licence a standard short identifier, such as MIT or Apache-2.0.
Licences fall into two broad groups. Permissive licences, such as MIT, BSD and Apache 2.0, let you use the code in closed products, mostly asking you to keep copyright and licence notices. Copyleft licences, such as the GPL family, require that if you distribute software built on the code, you share your source under the same terms. Some copyleft licences extend this to software offered over a network.
Why it matters
Licences decide what you can do with your own product. A copyleft component in the wrong place can force you to publish code you meant to keep private, and buyers or investors often ask for a licence list during due diligence. It also affects IP assignment, because the client owns the custom code but the open source parts stay under their own licences.
In a product build
A list of open source components and their licences belongs in the build's handover pack, next to the IP assignment.
Common mistakes.
- 01
Never checking licences of indirect dependencies, which is where surprises usually hide.
- 02
Treating "free to download" as "free to use any way you like".
- 03
Removing licence notices from shipped code, which most licences require you to keep.
Read the official text.
Primary sources this definition is based on.
- Open Source Initiative, The Open Source Definitionchecked 2026-10-25
- Open Source Initiative, OSI approved licenseschecked 2026-10-25
- SPDX License Listchecked 2026-10-25
Related terms.
- IP assignmentThe part of a contract that transfers ownership of code, designs and other work from the people who made them to the client.
- Handover (software handover)Moving the code, accounts, documents and know-how of a product from the team that built it to the team that will run it.
- Vendor lock-inWhen leaving a supplier, platform or tool would cost so much time or money that you are effectively stuck with it.
- SaaS (software as a service)Software you use over the internet, usually by subscription, while the provider runs the application and everything under it.
