Do you know ghouls from goblins and ghosts?
"vigor, energy," 1912, shortened form of pepper (n.), which was used in the figurative sense of "spirit, energy" from at least 1847. Pep rally is attested from 1945; pep talk from 1926. To pep (something) up is from 1925.
To stimulate; energize; brighten; JAZZ something UP: Pep up your winter wardrobe (1925+)