Open source software
Open source software is software whose copyright holder grants users the rights to use, study, and possibly modify and distribute it. Such software can be developed through open collaboration, where an unlimited number of specialists participate in the development online. This definition is recognized as a standard internationally.
Open source software development helps to harness different perspectives beyond the views of a single company. With open source, users can tailor software to their personal needs.
An important factor in open source software is the license, which defines the features, restrictions, and even compulsions when using the software. For instance, GPL licenses force to publish software modifications which the user has made, while keeping the underlying license of those modifications.
Examples of free software licenses: Apache License, BSD license, GNU General Public License (GPL), GNU Lesser General Public License, MIT License, Eclipse Public License, Mozilla Public License, etc.