talk about vs speak

talk about and speak both are verbs.

Word	Noun	Adjective	Verb	Adverb
talk about	No	No	Yes	No
speak	No	No	Yes	No

As verbs, speak is a hypernym of talk about; that is, speak is a word with a broader meaning than talk about:

Other hypernyms of talk about include mouth, talk, utter, verbalise, verbalize.

talk about (verb)	speak (verb)
to consider or examine in speech or writing	express in speech
discuss or mention	exchange thoughts; talk with
	use language
	give a speech to
	make a characteristic or natural sound