Meaning

originOnomatopoeic, variant of num, num-num. Attested 2004 as om nom, om nom nom, popularized from 2007 in internet use, second place in the American Dialect Society’s "Word of the Year" 2010. From the catchphrase of Cookie Monster on Sesame Street, as at the end of “C Is For Cookie” (1971), made when devouring cookies. However, as late as 2009, this was canonically written with a ‘u’, as in S is for…

Etymology from Wiktionary, CC BY-SA 3.0