What's the meaning of the word "nom"?
pls give me some examples about it's usage.
Thanks!

Question

Answer

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.

Answer

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.

Answer

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.