panel discussion vs discussion

panel discussion and discussion both are nouns.

Word	Noun	Adjective	Verb	Adverb
panel discussion	Yes	No	No	No
discussion	Yes	No	No	No

As nouns, discussion is a hypernym of panel discussion; that is, discussion is a word with a broader meaning than panel discussion:

panel discussion: discussion of a subject of public interest by a group of persons forming a panel usually before an audience
discussion: an exchange of views on some topic

Other hypernyms of panel discussion include give-and-take, word.

panel discussion (noun)	discussion (noun)
discussion of a subject of public interest by a group of persons forming a panel usually before an audience	an exchange of views on some topic
	an extended communication (often interactive) dealing with some particular topic