Learn what FOSS licenses are, why they matter, and the differences between popular open-source licenses.
May 28, 2025
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5 min read
If you're working with open-source software, you've probably come across terms like FOSS, GPL, MIT, or Apache License. But what do these licenses actually mean? How do they affect how you can use, modify, and distribute software?
In this blog, we'll break down what a FOSS license is, explore the most common types, and help you choose the right one for your project.
FOSS stands for Free and Open Source Software. A FOSS license is a legal framework that allows users to:
These freedoms are designed to promote transparency, collaboration, and innovation.
But "free" doesn't always mean "without restrictions." Different licenses impose different rules around what you must do when you share or modify the software.
FOSS licenses generally fall into two main categories:
These licenses have minimal requirements. You can use, modify, and redistribute the software with few obligations. You don't have to use the same license in your derivative work. They're ideal for maximum flexibility and are often business-friendly.
Popular permissive licenses include:
These licenses ensure that derivative works are also distributed under the same license. If you modify and distribute the software, you must release the source code under the same terms.
Popular copyleft licenses include:
License | Type | Key Requirement | Usable in Proprietary Software? |
---|---|---|---|
MIT | Permissive | Must include the original license | Yes |
Apache 2.0 | Permissive | Include notice and do not use trademarks | Yes |
BSD | Permissive | Include copyright and disclaimer | Yes |
GPL | Copyleft | Must open source derivatives under same license | No |
LGPL | Copyleft | Less strict; allows dynamic linking | Yes (with conditions) |
AGPL | Copyleft | Must release source even if software runs as a service | No |
Here's how you might include an MIT license header in a Python script:
Here are some general guidelines:
FOSS licenses are more than just legal jargon-they shape how software is shared, improved, and commercialized. Whether you're an open-source maintainer, contributor, or user, understanding these licenses empowers you to make informed, ethical, and strategic decisions.
Got a favorite FOSS license? Or a horror story about choosing the wrong one? Share your experience in the comments!