A bell tower (also belfry) is a tower

Tower

A tower is a tall structure, usually taller than it is wide, often by a significant margin. Towers are distinguished from masts by their lack of guy-wires....

 which contains one or more bell

Bell (instrument)

A bell is a simple sound-making device. The bell is a percussion instrument and an idiophone. Its form is usually a hollow, cup-shaped object, which resonates upon being struck...

s, or which is designed to hold bells, even if it has none. In the European tradition, such a tower most commonly serves as part of a church and contains church bell

Church bell

A church bell is a bell which is rung in a church either to signify the hour or the time for worshippers to go to church, perhaps to attend a wedding, funeral, or other service...

s. When attached to a city hall

City hall

In local government, a city hall, town hall or a municipal building or civic centre, is the chief administrative building of a city...

 or other civic building, especially in continental Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

, it is often named "belfry". Elsewhere, the term "belfry" refers strictly to the part of the tower which contains the bells.