The Free Software Foundation in its "Free Software Definition" defines four freedoms, according to which computer programs may be regarded as "Free Software", as long as they comply with these conditions. According to this definition the user has the freedom to use, adapt, copy and redistribute modified or unmodified copies of the software:

"Free software is a matter of the users' freedom to run, copy, distribute, study, change and improve the software. More precisely, it refers to four kinds of freedom, for the users of the software:

  • The freedom to run the program, for any purpose (freedom 0)
  • The freedom to study how the program works, and adapt it to your needs (freedom 1). Access to the source code is a precondition for this
  • The freedom to redistribute copies so you can help your neighbor (freedom 2)
  • The freedom to improve the program, and release your improvements to the public, so that the whole community benefits (freedom 3). Access to the source code is a precondition for this"

(Source: "The Free Software Definition")

 

GNU is a recursive acronym for "GNU's Not Unix"; it is pronounced guh-noo, like canoe.