# Software license

> The legal terms that say what you may and may not do with a piece of software.

- Level: Basic
- Topics: Software
- URL: https://tidbit.legios.com.ar/software-license/
- In Spanish: [Licencia de software](https://tidbit.legios.com.ar/es/software-license/)

A **software license** is the permission slip that comes with a program. Software is protected by copyright, like a book or a song, so by default you cannot copy, change or redistribute it. The license is the author's statement of which of those things you are allowed to do, and under what conditions.

**Proprietary** licenses, the long agreements you click through when installing Windows or Photoshop (an **EULA**, end-user license agreement), usually let you run the program and little else: no peeking at the source code, no copying, often a limit on how many computers. You are renting the right to use it, not buying the program.

Open source licenses go the other way and let anyone read, change and share the code, with different strings attached. **Permissive** licenses like **MIT**, Apache 2.0 or BSD ask for little more than keeping the author's name and the license text; you can even put the code inside a closed commercial product. **Copyleft** licenses like the **GPL** add one important condition: if you distribute a modified version, you must share your changes under the same license. Linux uses the GPL, which is why its improvements keep flowing back.

For companies this is not a formality. Mixing GPL code into a product you sell, or using a library whose license forbids commercial use, can mean having to publish your own code or facing a lawsuit. That is why many teams scan their dependencies' licenses automatically.

## An analogy

The rules that come with a rented apartment versus a gift. A lease says what you can and cannot do with the place; a gift with a note saying "do what you want, just mention me" is a permissive license; "keep it, but if you pass it on, pass it on with the same note" is copyleft.

## Keep in mind

- Software is copyrighted; the license says what you are allowed to do with it.
- Proprietary licenses (EULAs) usually allow only use, not copying or changing.
- Permissive licenses (MIT, Apache, BSD) allow nearly anything with credit.
- Copyleft licenses (GPL) require sharing modifications under the same terms.

## Go deeper

- [Choose an open source license (choosealicense.com)](https://choosealicense.com/)
- [Licenses approved by the Open Source Initiative](https://opensource.org/licenses)
- [Software license on Wikipedia](https://en.wikipedia.org/wiki/Software_license)

## Related terms

- [Source code](https://tidbit.legios.com.ar/source-code/): The human-readable text that programmers write and that a program is built from.
- [Open source](https://tidbit.legios.com.ar/open-source/): Software whose code anyone can read, use, change and share.
- [Linux](https://tidbit.legios.com.ar/linux/): A free, open source operating system that runs most of the internet's servers.