snogging vs kissing

snogging and kissing both are nouns.

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

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

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

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

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