What is a Frat party? Well, it's a party that's put on by a Fraternity. These parties are not to be confused with Bro Parties, and are sometimes well orchestrated productions. Lots of frat parties happen on Frat row.
Frat parties are usually the "type" of party you see in movies: dudes dancing on tables, tons of kegs, loud ghetto music. The beer always sucks at frat parties so don't expect to get drunk, unless of course you are in that Frat in which case you actually have a good time and know where the good stuff is. Frats don't enjoy spending money on stuff for people that are gonna come in for the freebies.
One of the advantages of being in a frat is that you can have the good stuff so the cheap crappy stuff is left for everyone else.