What is apse definition?

An apse is a semi-circular or polygonal recess that forms the endpoint of a building, usually a church or a temple. The term apse comes from the Latin "apsis," which means vault or arched recess. Historically, apses were used to hold the altar or religious icon and were used for formal ceremonies, such as the celebration of the Eucharist. They were often adorned with frescoes, mosaics, or sculptures, and were considered a commanding architectural feature. Apse vaults are typically semicircular, but can also be polygonal, or even rectangular in non-Christian religious architecture.