rally vs pep rally

rally and pep rally both are nouns.

Word	Noun	Adjective	Verb	Adverb
rally	Yes	No	Yes	No
pep rally	Yes	No	No	No

As nouns, pep rally is a hyponym of rally; that is, pep rally is a word with a more specific, narrower meaning than rally:

Other hyponyms of rally include revival, revival meeting.

rally (noun)	pep rally (noun)
(sports) an unbroken sequence of several successive strokes	a rally (especially of students) before a game
the feat of mustering strength for a renewed effort
an automobile race run over public roads
a large gathering of people intended to arouse enthusiasm
a marked recovery of strength or spirits during an illness

rally (verb)	pep rally (verb)
return to a former condition
harass with persistent criticism or carping
call to arms; of military personnel
gather
gather or bring together