A remote is a paintball accessory that allows one to remove the weight of a CO2, compressed air, or nitrogen tank from the marker and redistrubute the weight somewhere else, such as in a harness carried on the back or in the pocket of your pants, if you don't mind it bouncing around in there when you run. The remote is in effect an extension cord of sorts, a line connecting the air tank to the marker instead of connecting the tank to the marker directly.
Remotes are manufactured in several styles and are available in either braided steel or flexible plastic hose, as well as straight or telephone-cord-style curly. There isn't much variety when it comes to color; if you opt for the braided steel, you get a shiny silver braided steel hose, and if you choose the plastic, you get black.
A secondary advantage of the remote is that it functions as a partial expansion chamber when used on carbon dioxide powered markers. It allows extra room for the gas to expand and decreases the chance of the gas entering the marker in a liquid state.