Skipping one's classes or other academic obligations for an extended period of time in order to pursue other, more socially rewarding activities, such as drinking, golfing, and deep sea fishing. Other acceptable albeit less fratty activities include sleeping, movie-watching, and playing Call of Duty.
Zach showed up to Intro to Accounting for the first two weeks but then decided to go on fratbatical and wasn't seen until the final exam.
any extended period of leave from one's customary habit of always being on facebook, absorbing more meaningless drivel from people you haven't missed for years but are now somehow your FB friends, for the purpose of performing work, getting rest or to acquire new skills or training, etc. In other words, to get a life.