The Wii Balance Board is a mat used in Wii Fit and some other games. It is used for standing, push-ups, exercising, and many more activities.
The Board is split into four segments aesthetically, and senses the player's center of gravity over the board based on the pressure exerted on the board by the player's feet. Like a Wii Remote, the board uses a bluetooth connection to the Wii or Wii U, and can be synced by pressing the button on the back of the board. This accessory could be compared to the Power Pad for the NES. The board also comes packaged with four extra feet, which can be placed over the bottom of the original feet.