Gyro is the name for R.O.B.'s Down B Special Move in Super Smash Bros. Brawl. The attack resembles a spin toy that R.O.B. fires. It is somewhat chargeable; the longer you charge it, the stronger and faster it becomes. A fully charged Gyro normally does 18% of damage, and has high knockback. After you throw it, you can pick it back up and throw it at the opponent doing 10% of damage. You can only have one Gyro on the screen at any time and it takes a few seconds to regenerate if the Gyro is tossed offscreen. If R.O.B. cannot reuse his Gyro, he goes into his Gyro-charging stance and makes a motion with his arms as if to spin the Gyro, but no Gyro appears.
The "Gyro" is essentially a spinning top. The R.O.B. accessory for the Nintendo Entertainment System was able to spin up gyros and use them to press buttons to activate in-game effects for the game Gyromite; the button would remain pressed only as long as the gyro retained enough speed to remain upright.