Spinning is a move that Mario can perform in Super Mario Galaxy. It is done when the player shakes the Wii Remote (or Nunchuk for left-handed players). The move is slightly like a Spin Jump or Mario Tornado except that it can also be done on the ground. It can be used to reflect projectiles flying at Mario, stun enemies, activate switches, swim faster, and even pick up nearby items. Mario also ascends very slightly whenever he does a spin.
Mario is able to do a spin because of Luma, a white Luma given to Mario by Rosalina. Whenever Mario does a spin, Luma pops out of his hat for a second. Mario can only perform a spin once in the air. He must touch solid ground before he can use the ability again. Even on the ground there is a slight recharge time for this move. When Luigi uses this move, a slightly longer recharge time is required.
An extremely useful application of the spin is the ability to stun, freeze, or make enemies dizzy by spinning into them. This gives Mario a chance to escape or attack the enemies if the player is fast enough. Spinning is needed to defeat some bosses.
It also appears that after his first defeat in Super Mario Galaxy, Bowser took note of Mario's spin move, and made his own version.