substance a young child cheerfully picks out of his father's belly button
Junior, I've got a present for you - some gradu in my belly button.
Gradu (pronounced gra-DOO) = Any unwanted substance. There are two types:
1. Specific gradu: You know what it is (e.g., the brown residue that is left at the bottom of your coffee cup after you have been gone for a few days ... It's dried coffee!)
2. Non-specific gradu: You don't know what it is (e.g., the round, wrinkled, grayish fuzz-covered object you find in your vegetable drawer after being gone all summer).
Man, that was some gnarly gradu somebody left under the couch; it trapped all the dust bunnies! Yuck!