snogging vs petting

snogging and petting both are nouns.

Word	Noun	Adjective	Verb	Adverb
snogging	Yes	No	No	No
petting	Yes	No	No	No

As nouns, petting is a hypernym of snogging; that is, petting is a word with a broader meaning than snogging:

snogging: (British informal) cuddle and kiss
petting: affectionate play (or foreplay without contact with the genital organs)

Other hypernyms of snogging include caressing, cuddling, fondling, hugging, kissing, necking, smooching, snuggling.

snogging (noun)	petting (noun)
(British informal) cuddle and kiss	affectionate play (or foreplay without contact with the genital organs)