What is Rallying ?

What is rallying?  We are only in our third year of caravanning and have never rallied. We are curious though, we've read a number of threads and there's lots of talk of "joining in", "youth sections", "entertainment thrown in", "activities laid on", "paricipating", "cliques", "option of not joining in" and so on ..... but I cant seem to find what folk are actually doing, is it just a social gathering ?. Anybody like to do a typical 'day in the life' of a rallier ?