Open source (http://www.opensource.org/) is computer software for which:

• the source code is available to the end-user;
• the source code can be modified by the end-user;
• there are no restrictions on redistribution or use;
• the licensing conditions are usually intended to facilitate continued re-use and wide availability of the software, in both commercial and non-commercial contexts;
• the cost of acquisition to the end-user is often minimal.