Free software, as defined by the Free Software Foundation (FSF), is software which can be used, copied, studied, modified and redistributed without restriction. Freedom from such restrictions is central to the concept of free software, such that the opposite of free software is proprietary software, and not software which is sold for profit, such as commercial software. Free software may sometimes be known as libre software, Floss, or open source software.

Most free software is distributed gratis online, or off-line for the marginal cost of distribution, but this is not required, and people may sell copies for any price. The capitalized term "Open Source" is attached to a definition originally created in 1998 from Debian's rewrite of the GNU definition of Free Software. As a result, nearly all Open Source programs are Free Software, but there are some exceptions.

Freeware is software made available free of charge, but is generally proprietary, as users do not have the freedom to use, copy, study, modify or redistribute. Source code for freeware may or may not be published, and permission to distribute modified versions may or may not be granted, so freeware is gratis, and not libre software.