thumb|300x300px|Cathedral ground plan. The shaded area is the transept; the darker shading at the centre represents the [[Crossing (architecture)|crossing.]]
thumb|South transept at [[Kilcooly Abbey, County Tipperary, Ireland]]
A transept (with two semitransepts) is a transverse part of any building, which lies across the main body of the building. In cruciform ("cross-shaped") churches, particularly within the Romanesque and Gothic traditions of Christian church architecture, a transept is an area set crosswise to the nave. Each half of a transept is known as a semitransept.