overlap vs co-occurrence

overlap and co-occurrence both are nouns.

Word	Noun	Adjective	Verb	Adverb
overlap	Yes	No	Yes	No
co-occurrence	Yes	No	No	No

As nouns, co-occurrence is a hypernym of overlap; that is, co-occurrence is a word with a broader meaning than overlap:

overlap: the property of partial coincidence in time
co-occurrence: the temporal property of two things happening at the same time

Other hypernyms of overlap include coincidence, concurrence, conjunction.

overlap (noun)	co-occurrence (noun)
a flap that lies over another part	the temporal property of two things happening at the same time
the property of partial coincidence in time	an event or situation that happens at the same time as or in connection with another
a representation of common ground between theories or phenomena

overlap (verb)	co-occurrence (verb)
extend over and cover a part of
coincide partially or wholly