HTML5 track element question

Question

Can someone explain what the track element in HTML is for in very simple terms?

Answer 1

Apologies for shameless self promotion, but I wrote an article about the track element for HTML5 Rocks: Getting Started With The Track Element.

EDIT: removed examples from post: as Jörn pointed out (see below) Chrome was crashing if you scrolled a video with a track element offscreen. This seems to have been fixed now (in 19.0.1053.0 canary) but I'll leave the examples out for the moment.