The two main types of Aids to Navigation are buoys and beacons.
Buoys are Aids that float on top of the water, but are moored to the bottom of the
body of water. Some have a light affixed to the top; some do not. It’s important to understand them and their purpose.
A buoy with a cylindrical shape and a conical top is referred to is a “nun.”
A buoy with a cylindrical shape and a flat top is called a “can.”
Beacons are Aids that are permanently fixed, most commonly to the bottom of a
body of water. A beacon that has a light attached is simply referred to as a “light”;
a beacon without a light attached is called a “daybeacon.”
Both buoys and beacons can provide variety of navigation information via shape, color, light, and/or audible signal.
Dayboards are informational signboards.
The term topmark refers to a non-lighting element, such as a sphere, that may be affixed to the top of an Aid.