The Debian Free Software Guidelines (DFSG) is a set of guidelines that the Debian Project uses to determine whether a software license is a free software license, which in turn is used to determine whether a piece of software can be included in Debian. The DFSG is part of the Debian Social Contract.
The guidelines
Free redistribution.
Inclusion of source code.
Allowing for modifications and derived works.
Integrity of the author's source code (as a compromise).
No discrimination against persons or groups.
No discrimination against fields of endeavor, like commercial use.
The license needs to apply to all to whom the program is redistributed.
License must not be specific to a product.
License must not restrict other software.The GNU GPL, BSD, and Artistic licenses are examples of licenses considered free.
History
The DFSG was first published together with the first version of the Debian Social Contract in July 1997.
The primary author was Bruce Perens, with input from the Debian developers...