English Newbie Question

[SIMIN]

Hello,
I am new to English and there are some words that I see here and there but never can find them in any dictionary!
Can anyone please tell me what are these 3 words, for example?
I am so curious about them!

Omerta
Bon Appetit
Creme de la Creme

 

[Nate Bross]

Omerta
-- Code of silence? [not sure on this one]

Bon Appetite
-- means "enjoy"

Creme de la Creme
-- best of the best