Verb, intransitive and (less commonly) transitive. Kiss, especially in a vigorous or passionate manner; make out. Thus, Martin Amis, The Rachel Papers (1973): “They were enjoying a kiss—well, more of a snog really.” American popularity was certainly aided by Bridget Jones’ s Diary (1996), Angus, Thongs and Full-Frontal Snogging (2001), and other trans-Atlantically popular examples of British chick lit. Google Ngram.
And when couples do start smooching or snogging, they usually get interrupted — partly because [schlock Hollywood director Andy] Milligan throws so many prying characters into the cage of his film frame. (Richard Corliss, Time, November 30, 2011)/We already know that Matt Damon will be playing Michael Douglas’ gay lover in the upcoming biopic Liberace, but now they’ve both confirmed there will be a good bit of guy-on-guy snogging for the big screen. (Tampabay.com, March 23, 2011)