Free software, as defined by the Free Software Foundation, is software which can be used, copied, studied, modified and redistributed with little or no restriction. Freedom from such restrictions is central to the concept, with the opposite of free software being proprietary software (a distinction unrelated to whether a fee is charged). The usual way for software to be distributed as free software is for the software to be licensed to the recipient with a free software license (or be in the public domain), and the source code of the software to be made available (for a compiled language).

By contrast, “Freeware” is software made available free of charge, but is generally proprietary, as users do not necessarily have the freedom to use, copy, study, modify or redistribute it. Source code for freeware may or may not be published, and permission to distribute modified versions may or may not be granted, so freeware is gratis, but not necessarily libre software. Free software is entirely compatible with commercial software: a prohibition on selling the software would be a restriction failing the free software definition.