Its a pole that swings around typically on the driver side of your pickup. Welders will hang their leads, grinder/buffing wheel and or umbrella from this pole. Pipeline welders usually have a hoosier pole on thier trucks so they dont have to put their leads or grinders on the back of their truck each time they pull up to weld another joint. Most hoosier poles telescope in and out so you can adjust it to the proper length you need while pipelining and will fold away on the back of the welders truck while not in use. A very handy device to have on the back of your truck.