Alternative terms for free software, such as open source, FOSS, and FLOSS, have been a controversial issue among free software users from the late 1990s onwards. Coined in 1983 by Richard Stallman, "free software" is used to describe software which can be used, modified, and redistributed with little or no restriction. These freedoms are formally described in The Free Software Definition, first published in February 1986.

Alternatives for "free software" were sought for marketing purposes and because of a perceived "moralising and confrontational" attitude that had been associated with the term.^{[by whom?]} In addition, the "available at no cost" ambiguity of the word "free" was seen as discouraging business adoption. In a 1998 strategy session in California, "open source software" was selected by Todd Anderson, Larry Augustin, Jon Hall, Sam Ockman, Christine Peterson, and Eric S. Raymond. Richard Stallman had not been invited. The session was arranged in reaction to Netscape's January 1998 announcement of a source code release for Navigator (as Mozilla). Those at the meeting described "open source" as a "replacement label" for free software and Open Source Initiative was soon-after founded by Eric Raymond and Bruce Perens to promote the term as part of "a marketing program for free software". Stallman and others object to the term "open source software" because it does not make people think of the freedoms that the software in question gives users.

Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients have the same rights under which it was obtained and that manufacturers of consumer products incorporating free software provide the software as source code. The word free in the term free software refers to freedom (liberty) and is not at all related to monetary cost. The Free Software Foundation advises people to "avoid using terms like 'give away' or 'for free,' because those terms imply that the issue is about price, not freedom." Free software is generally available without charge but is not bound to such a restriction.

Fees are usually charged for distribution on compact discs and bootable USB drives, or for services of installing or maintaining the operation of free software. Development of large, commercially-used free software is often funded by a combination of user donations, corporate contributions, and tax money. The SELinux project at the United States National Security Agency is an example of a federally-funded free software project.

Chroma key compositing, or chroma keying, is a special effects / post-production technique for compositing (layering) two images or video streams together, used heavily in many fields to remove a background from the subject of a photo or video - particularly the newscasting, motion picture and videogame industries. A color range in the top layer is made transparent, revealing another image behind. The chroma keying technique is commonly used in video production and post-production. This technique is also referred to as color keying, colour-separation overlay (CSO; primarily by the BBC), or by various terms for specific color-related variants such as green screen, and blue screen - chroma keying can be done with backgrounds of any color that are uniform and distinct, but green and blue backgrounds are more commonly used because they differ most distinctly in hue from most human skin colors and no part of the subject being filmed or photographed may duplicate a color used in the background. It is commonly used for weather forecast broadcasts, wherein the news presenter appears to be standing in front of a large map during live television newscasts, though in actuality it is a large blue or green background. When using a blue screen, different weather maps are added on the parts of the image where the color is blue. If the news presenter wears blue clothes, his clothes will also be replaced with the background video. A complementary system is used for green screens. Chroma keying is also used in the entertainment industry for special effects in movies and videogames. The advanced state of the technology and much commercially available computer software, such as Pinnacle Studio, Adobe Premiere, and dozens of other computer programs, makes it possible and relatively easy for the average home computer user to create videos using the "chromakey" function and easily affordable greenscreen or bluescreen kits.