Open-Source

Glossary Term Definition:

Software can be considered open-source when it complies with the crieteria of the Open Source Initiative. Briefly summarized: to be considered open-source, the software or license must...

...be distributable and redistributable free of charge
...be distributed with uncompiled source code
...allow modifications and derived works
...restrict modifications and derived works only in the event of further development by the original author
...not discriminate against any person or group
...not discriminate against any field, profession, or endeavor
...be usable without acquisition of an additional license
...not be restricted to use as part of a larger software package
...not restrict the use of other software
...not be predicated on any individual technology or style of interface

A more detailed list of these conditions may be found here.