What term describes any buoy that is smaller than a lighthouse buoy and has a tall central structure?

The term that describes any buoy that is smaller than a lighthouse buoy and has a tall central structure is "pillar." Pillar buoys are characterized by their vertical design and are typically used to mark channels, hazards, or specific areas in navigable waters. Their distinct tall and slender shape helps them to stand out against the horizon and provides clear visibility for mariners.

Other terms mentioned, such as marker and floating buoy, refer to broader categories without the specific characteristics associated with pillar buoys. A marker can denote various types of navigational aids, including buoys and beacons, while a floating buoy generally indicates a buoy that simply floats on the surface of the water without the tall, central structure. A pole buoy, though somewhat similar, typically refers to a structure that is mounted vertically but may not be described specifically with the same emphasis on its height relative to being a smaller version of a lighthouse buoy. Thus, "pillar" is the most accurate term in this context.