As Sparky said, it's a setting under the remote control menu. First click of the remote then raises the mirror, and the second shoots. It's pretty much the constant when I'm using a remote.
When tripod mounting a camera for long exposure, you use Mirror Up to first move the mirror up, then allow the camera to stop moving before you open the shutter. It takes the raising of the mirror out of the equation and prevents the 'mirror slap' from causing vibration and possibly moving the camera when the shutter is open.. which would cause motion blur.