A keynote speaker in the functional sense is a person who delivers a keynote speech, i.e. a person who gives a speech, which receives increased attention because of its significance in terms of content, type of presentation or popularity of the speaker.
A keynote speaker in the professional sense is a person who regularly delivers keynotes as part of his or her professional activity, i.e. a person who offers the paid service of holding speeches, lectures and presentations, which are suitable to take a prominent position in events of the client.