noun an aerial manouvre performed off a diving board involving making first contact with the water surface with the buttocks, or a single piece of buttock. The bummy results in a imposing display of man and water that onlookers will find awe inspiring and will create a sonic boom so powerful it has bee known to blast bikini tops off nearby BummyHo's.
It is also polite and acceptable to enquire after witnessing a bummy how many pairs of shorts the bummy artist was wearing before you dive in.
Not to be confused with an old man who writes books under the pseudonym 'Bummy'
"hey bro, you rockin' 4 pairs of boardies for that bummy??"
"nah man, that shit was raw"