http://en.wikipedia.org/wiki/Open_Source_Definition
Under the Open Source Definition, licenses must meet ten conditions in order to be considered open source licenses
- Free Redistribution: the software can be freely given away or sold.
- Source Code: the source code must either be included or freely obtainable.
- Derived Works: redistribution of modifications must be allowed.
- Integrity of The Author’s Source Code: licenses may require that modifications are redistributed only as patches.
- No Discrimination Against Persons or Groups: no-one can be locked out.
- No Discrimination Against Fields of Endeavor: commercial users cannot be excluded.
- Distribution of License: The rights attached to the program must apply to all to whom the program is redistributed without the need for execution of an additional license by those parties.
- License Must Not Be Specific to a Product: the program cannot be licensed only as part of a larger distribution.
- License Must Not Restrict Other Software: the license cannot insist that any other software it is distributed with must also be open source.
- License Must Be Technology-Neutral: no click-wrap licenses or other medium-specific ways of accepting the license must be required.
Anything else might be considered free of charge, but is not open source. Just a reminder.
