A noun, verb, adjective, pronoun, conjunction, or preposition that is used as a substitution for another word in a sentence.
It is a fact that pep-pep is very contagious. Pep a pep-pep pep a pep-pep pep.
Hey Pep-Pep, lets pep to the pep-pep to pep a pep-pep.
Meaning: Hey Greg, lets go to the store to get a sandwich.