bull session vs conference

bull session and conference both are nouns.

Word	Noun	Adjective	Verb	Adverb
bull session	Yes	No	No	No
conference	Yes	No	No	No

As nouns, conference is a hypernym of bull session; that is, conference is a word with a broader meaning than bull session:

bull session: an informal discussion (usually among men)
conference: a discussion among participants who have an agreed (serious) topic

Other hypernyms of bull session include group discussion.

bull session (noun)	conference (noun)
an informal discussion (usually among men)	a discussion among participants who have an agreed (serious) topic
	a prearranged meeting for consultation or exchange of information or discussion (especially one with a formal agenda)
	an association of sports teams that organizes matches for its members