Chandrashala is the term most often used to describe the circular or horseshoe arch that decorates so many Indian cave temples and shrines. The arch is shaped like the cross-section of a barrel vault.
When used on the facade of a chaitya hall, it is called a chaitya arch. It is sometimes called a gavaksha (or kudu, in Tamil) when used as a decorative element on a structural temple.
Examples include Ellora Caves 9, Ajanta Caves 9 and 19 and Varaha Cave Temple at Mamallapuram.
Source: Wikipedia