1. (noun) Yet another slang word for booty. Only booties of immense size deserve this title. The root word of valumper is LUMP, which is referring to the lumps of the individual booty cheeks.
2. Can also be used in verb form, "to valump"

Internet persona(s) who happens to follow you and you happen to follow them back and maintain communication with and have a mutual liking for eachother whether it be friendship wise, etc. (Mutuals if more than one mutual)