While the specific freedoms may vary, OSS licenses are generally categorized as (1) permissive licenses or (2) restrictive (also known as reciprocal, viral or copyleft) licenses.

Permissive licenses (like the Apache 2.0, BSD, MIT) provide licensees with the right to freely modify, adapt and combine the OSS code with proprietary code to create derivative works that do not contain major restrictions on such modifications or how resulting works can be subsequently licensed.

On the other hand, restrictive licenses (like the GPL, AGPL, LGPL) go further in imposing requirements for licensees to in turn re-license their specific developments under the original license (and as a condition, also make the modified source code available). While the provisions vary, most restrictive OSS license terms will to some extent apply not only to the original source code and software, but to any derivative works based on it. To the extent OSS licensed in a restrictive manner is used alongside proprietary projects for which source code is meant to be closed or not available to the public, owners must be careful not to unintentionally have their own software be made subject to licensing under the open source license terms.