In order to have a reverse gear, they would need a transmission, and an engine attached to it. Which they don't. Wheels on an airplane move freely, and are only equipped with brakes. The airplane moves using jet thrusters, or propellers. read more
Many jet airliners and cargo planes also have reverse thrust, and in some cases it CAN be used to back up, but in most companies it is forbidden by company policy, for the reasons given. So in that sense, airplanes DO have reverse gear, but it isn't called that. read more