Okay let me take a stab at explaining what a frat house is.
A frat house is a house, at a university campus, and basically you can live there if you are a member of the fraternity or sorority (which is basically paying $$ for friends
no offense to anyone in here who may have been in one
) But basically yeah.
So a frat house, is the house where a lot of members of a certain fraternity live... usually a lot of partying, sex, drinking etc goes on inside
Since fraternities are normally known by their Greek letters, there would usually be the letters on the outside... and a frat house can usually be spotted by large numbers of boys on the front lawn playing sports
I don't know if that helps.