Autoguiding is using a separate camera from your main imaging camera to make your tracking more accurate during long exposures for deep sky astrophotography. When done properly, autoguiding can increase your exposure length by roughly 5x longer before star trails begin to occur. Autoguiding works by using the guide camera to watch a star, and if that star begins to drift by even a pixel, it can communicate with your tracking mount to make the necessary corrections. It makes these tiny corrections while your main camera is exposing, so you end up with a sharp image without any star trails. There are two main ways to do autoguiding: with a guide scope, which is like a mini telescope that sits on top of your main telescope, or with an off-axis guider.