A double Aggie is a student or alumnus of a U.C. Davis graduate program who also attended UCD as an undergraduate. Beyond this most basic definition, the precise requirements to be a double Aggie are unclear. The majority view holds that one must have previously received a bachelor's degree from UC Davis, and then received or be working towards a graduate degree from UCD to qualify. The minority view holds that taking any graduate classes after being enrolled as an undergraduate is sufficient.
Some double Aggies have never heard of the term. Go figure.