Noun. A derogatory term for anyone of a minority group, especially a visible minority. Used by politically-minded Canadians with a prejudicial bent. The term is taken from Section 15 of the Canadian Charter of Rights and Freedoms, which prohibits discrimination on the basis of ethnicity, nationality, race, sexual orientation, etc.
Basically, a Section 15 is anyone who does not fit into the general majority.
"That gay, black, Jewish guy is such a Section 15."
"Dude, that's like, racist."