Letter representation; Text description "arc". In mathematics, a semicircle can be represented by letters, such as "semicircle AB" or "semicircle ABC", where "A" and "B" respectively represent two endpoints of a semicircle. In narrative, a semicircle can be represented by an "arc". A semicircle refers to the half of a circle, that is, the part whose central angle is 180 degrees. In geometry, a semicircle can be represented by an arc.