Big Red Freakout!
Obligatory reference to The Matrix
Unfortunately, no one can be told what the Freakout is. You must experience it for yourself.
Actually Useful Information
Freakout is probably best described as being analogous to Homecoming. Only instead of being in the Fall, it's in late January or early February, and instead of a football game, it's a men's hockey game. It is traditional for a large number of alumni to return for Freakout and for a gift to be given to every person in attendance by the Athletic Department. For a further list of traditions associated with Freakout, see Freakout Traditions.
See the category Freakout for info on Freakouts of the past.