de gorra

From the custom at the University of Salamanca in the 16th century of rich students paying poor students for various tasks; the poor students were also invited to eat for free at banquets, where they stood out from the rich students by wearing simple caps (gorras).[1]

de gorra

1. (idiomatic) on someone's dime, at the expense of someone else

• “de gorra”, in Diccionario de la lengua española, Vigésima tercera edición, Real Academia Española, 2014