There are many structures which may have clocks or clock faces attached to them and some structures have had clocks added to an existing structure. According to the Council on Tall Buildings and Urban Habitat a building is defined as such if at least fifty percent of its height is made up of floor plates containing habitable floor area. Structures that do not meet this criterion, are defined as towers. A clock tower historically fits this definition of a tower and therefore can be defined as any tower specifically built with one or more (often four) clock faces and that can be either freestanding or part of a church or municipal building such as a town hall. Not all clocks on buildings therefore make the building into a clock tower.

The mechanism inside the tower is known as a turret clock. It often marks the hour (and sometimes segments of an hour) by sounding large bells or chimes, sometimes playing simple musical phrases or tunes. (source)