festival vs celebration

festival and celebration both are nouns.

Word	Noun	Adjective	Verb	Adverb
festival	Yes	No	No	No
celebration	Yes	No	No	No

As nouns, celebration is a hypernym of festival; that is, celebration is a word with a broader meaning than festival:

festival: an organized series of acts and performances (usually in one place)
celebration: any joyous diversion

Other hypernyms of festival include festivity.

festival (noun)	celebration (noun)
an organized series of acts and performances (usually in one place)	any joyous diversion
a day or period of time set aside for feasting and celebration	the public performance of a sacrament or solemn ceremony with all appropriate ritual
	a joyful occasion for special festivities to mark some happy event