A fork of Rural Dictionary
a cute name for grandpa, as spoken by a young child. really. it sounds cute when a little kid says it. may be derived not just from the inability to clearly pronounce the word 'grandpa' but also due to some cosmic consciousness reference to drums (pa rump a pum pum) which relates the coolness of grandpas to drumming.
"Hey Pum Pum! Help me get my toys!"