web log vs diary

web log and diary both are nouns.

Word	Noun	Adjective	Verb	Adverb
web log	Yes	No	No	No
diary	Yes	No	No	No

As nouns, diary is a hypernym of web log; that is, diary is a word with a broader meaning than web log:

web log: a shared on-line journal where people can post diary entries about their personal experiences and hobbies
diary: a daily written record of (usually personal) experiences and observations

Other hypernyms of web log include journal.

web log (noun)	diary (noun)
a shared on-line journal where people can post diary entries about their personal experiences and hobbies	a personal journal (as a physical object)
	a daily written record of (usually personal) experiences and observations