A telecommunications tower is a structure more substantial than a mast, which is designed to hold electromagnetic transmission equipment high off the ground. A tower must either be capable of supporting a stairway or an elevator, or it must possess enough structural or architectural girth to distinguish it from a mast. Towers are necessarily self-supporting, and must not rely on lateral wires for stabilization.

Many telecommunications towers have observation decks or restaurant pods high on the structure, generally below the antenna. Because the structures are built primarily for signal transmission, these are not listed as observation towers.

The tower must support a stairway or elevator, or have enough structural or architectural bulk to distinguish it from a mast. An observation deck can be an additional facility without replacing signal transmission as the primary design purpose.