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1 definition by SeaCaptainDrake

 
1.
Boo
A scary ghost creature in the Mushroom Kingdom. Mario faces these a lot. These pearly-white ghosts will become invisible if anyone faces them. They usually cannot be disposed of. There are also other Boos, like the Big Boo, King Boo, and more.
"I thought I heard a Boo, but I turned around and saw nothing."
by SeaCaptainDrake December 06, 2003