A pylon is a bar or rod that supports some structure, like a bridge or a highway overpass. You might notice the pylons underpinning your city's elevated train tracks.
Pylons are often made of steel or concrete, because they are strong substances that can hold a large amount of weight. A pylon needs to be sturdy, since it is supporting a bridge, road, or power lines. Other pylons act as navigational aids, marking paths for cars or small planes. The word's original meaning was "gateway to an Egyptian temple." Pylon is a Greek word that means "gateway," from pyle, "gate or entrance."