Tympanum

In architecture, a tympanum (plural, tympana; from Latin and Greek words meaning "drum") is the semi-circular or triangular decorative wall surface over an entrance, door or window, which is bounded by a lintel and an arch.  It often contains sculpture or other imagery or ornaments.

Most architectural styles include this element.

For a good example in my work, see Krishna Slaying the Demon Kamsa, Banteay Srei, Angkor, Cambodia. 2019.

See also Angkor Architectural Styles.