A half-graben is a type of geological structure formed by extensional tectonics, where one side of a fault is down-dropped, creating a basin that is fault-bounded on one side. Half-grabens are significant in the study of rift systems, sedimentary basin development, and the tectonic evolution of extensional terrains.
Source McClay, K. R. (1990). Extensional Fault Systems in Sedimentary Basins: A Review of the Geometry, Processes, and Evolution. AAPG Memoir 46.