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Similar to Side Boob, Side Bum is the visual conception of the bare waste of a woman(or if an unfortunate situation, a man), while the back and front of the waist is visually obstructed or concealed, yet still revealing the curvature of the buttocks.
(Person A): I don't understand why people fixate over the Princess Leia bikini, that cloth she's wearing over her waist covers everything!

(Person B): Except when she points her hips towards the camera and reveals some major side bum.
by RapidEyeMovementOfTheTiger January 25, 2011
A term used when cleaning the toilet.
Did you clean that sidebum?
by Sidebottom May 17, 2008