This is, by its literal definition, a reference to a big drum. The practice of Bodu Beru is a performance that is generally conducted by three drummers and a lead singer. They tell the tales of ancient times that bring back the memories of hero's, romance and sacrifice.
When combined with the beats of the drum, it becomes a hypnotic thrum that keeps pulling you in. Be warned, it is expected that you get on your feet and get dancing as the crescendo gets closer.