This is when a character reveals that she or he was educated in (or is being educated in) a field or subject that is unexpected for the character. Typically, this gag takes the form of a college minor, as per the title suggests.
For example, a tough macho man could minor in Women's Studies or a ditzy society girl is minoring in Particle Physics.
A great, if narratively cheap, way to showcase [...] [tvtropes.org]