I've seen a commercial on the TV with a dog going "Nom nom nom..." (Going = 'saying' / making a noise) The dog had a very tasty dinner. "Nom nom nom yom yum num nom nom.... " I think I make the same noises when eating chocolate cake.

As Peachey says, 'nom' is a 'pretend' word which imitates the sound of someone enjoying eating something. It is also the French word for 'name'. You sometimes come across this in English sentences which have French phrases in them.

It mimics the sound of eating: om nom nom In a slang sense, I've seen it used as a verb (ie. to eat) as well as a noun (food/snacks). http://www.maniacworld.com/nom-nom-nom-song.html It's a cutesy word; not standard English at all.