Dhating Naach is a song from the film Phata Poster Nikla Hero.
Dhating actually isn't a standard word, though here it is used to express fun, the kind where you dance like anything, and without thinking of anything else. Naach of course means dance and hence dhating naach simply means dance with energy, dance uninterrupted.
Dhating can be considered equivalent to Dhinchak, Dhan te Nan, etc., which themselves don't have much meaning, but are used quite commonly.