Wikipedia's definition of dice stacking:
"Dice stacking is a performance art, akin to juggling or sleight-of-hand, in which the performer scoops dice off a flat surface with a dice cup and then sets the cup down while moving it in a pattern that stacks the dice into a vertical column via centripetal force and inertia."
YouTube is littered with dice stacking videos, my two personal favorite stackers perform below. The first kid demonstrates his skills with charming nonchalance, sipping his soda, whereas the second pro shows off a variety of techniques.
Scroll all the way down for a tutorial if you're interested in picking up the art yourself.