DFSG

Debian is especially well-known for its package management system, based on .deb packages handled by the dpkg and APT programs, which allows relatively painless upgrades from older versions of Debian, nearly effortless installs of new packages, and clean removal of old ones.
..... Click the link for more information.  Project uses to determine whether a software license is free software license Generally speaking, free software license is a phrase used by the free software movement to mean any software license that grants users of the software the following four freedoms:

1. The freedom to run the program for any purpose
2. The freedom to study and modify the program
3. The freedom to copy the program
4. The freedom to redistribute modified versions of the program

A license which preserves those freedoms for modified works is a copyleft license. See Free software movement for more information.
..... Click the link for more information. , which in turn is used to determine whether a piece of software can be included in the main, free software The term free software is used in essentially two different ways:

1. software that can be copied, used, studied, modified, distributed, etc., with few or no restrictions (think free speech and free market).
2. software which may be copied and used without payment (think free beer), also refered to as freeware (or gratis software).

These definitions may conflict and a piece of software that is free in the first sense may not be free in the second, and vice versa.
..... Click the link for more information.  distribution of Debian.

The guidelines state these requirements:

• free redistribution
• inclusion of source code
• modifications and derived works
• integrity of the author's source code (as a compromise for the likes of TeX

  T_EX (usually written TeX in plain text) is a typesetting system written by Donald Knuth, which is popular in academia, especially in the mathematics, physics and computer science communities. It has largely displaced Unix troff, the other favored formatter, in many Unix installations.

  TeX is generally considered to be the best way to typeset complex mathematical formulas, but, especially in the form of LaTeX and other template packages, is now also being used for many other typesetting tasks. It can be used to compose mathematical expressions on Encyclopedia pages;
  ..... Click the link for more information. )

• no discrimination against persons or groups
• no discrimination against fields of endeavor, like commercial use
• distribution of license, it needs to apply to all to whom the program is redistributed
• license must not be specific to Debian, basically a reiteration of the last point
• license must not contaminate other software

Example licenses are GPL

The GNU General Public License is a copyleft free software license. It is also referred to as the GNU GPL or, when there is no risk of confusion with other "general public licenses," simply the GPL.

In contrast to proprietary licenses, the purpose of the GPL is to protect the user's freedom rather than restrict it. It attempts to secure this through copyleft, unlike the BSD License or the MIT License. The GPL also qualifies as an open source license.
..... Click the link for more information. , BSD

BSD originally stood for "Berkeley Source Distribution". The BSD License is the license agreement that the BSD software (largely, a version of UNIX) is distributed under. The owner of the original BSD distribution was the "Regents of the University of California". This is because BSD originally came from the University of California, Berkeley.

Versions of the current BSD template (and the older version with the advertising clause) are often used by other organizations. The BSD License does not prohibit the use of the material licensed in products for resale. A notable example of this is the use of BSD networking code in Microsoft products, or the use of numerous FreeBSD components in MacOS X.
..... Click the link for more information. , and Artistic Artistic license is a colloquial term used to denote the liberties an artist may take in the name of art - for example, if an artist decided it was more artistically "correct" to portray St. Pauls Cathedral next to the Houses of Parliament in a scene of London, even though in reality they are not close together, that would be artistic license.

For Artistic License, a type of license used for some kinds of free software, see Artistic License. This name is a pun on the original usage.