An onion dome is a dome which bows out at the base and comes to a point at the top. It is often used in churches, and topped by a cross. This form of dome is most common in the architecture of central and eastern Europe and the former Byzantine Empire.

The swelling profile and pointed termination give the dome its onion-like outline. A round dome without that outward bow and narrowing point has a different form.

A cross is a common addition on churches, but it is not part of the required dome shape. The feature can therefore be present on another building use or without a cross.