The Constitution of the United Federation of Planets was a legal document which defined the fundamental political principles of the United Federation of Planets. It contained at least twelve "Guarantees" related to fundamental individual rights of citizens.
The Twelfth Guarantee of the Constitution dealt with the rights of artists, and defined an artist as "a person who creates an original artistic work." (VOY: "Author, Author")
In some instances those protections related to fundamental rights can be extended to non-citizens while on Federation territory (such as a Starfleetvessel). (TNG: "The Perfect Mate")
The relationship between the Constitution of the United Federation of Planets and the Charter of the United Federation of Planets is unclear. Both contain rights for individuals; as Sisko put it in DS9: "Accession": "caste-based discrimination goes against the Federation Charter". It is most likely that the Charter describes the requirements for entry of a planet into the Federation (e.g., no entry if caste-based discrimination is in place), while the Constitution describes the principles, governing structure, and citizen rights once becoming a member (e.g., rights against self-incrimination).