Terrain Awareness Warning System (TAWS)

An on-board, terrain proximity alerting system providing the aircrew "Low Altitude warnings" to allow immediate pilot action. (PCG definition)

A timed-based system that provides information concerning potential hazards with fixed objects by using GPS positioning and a database of terrain and obstructions to provide true predictability of the upcoming terrain and obstacles. (PHAK definition).

Source: PCG, Pilot Handbook of Aeronatical Knowledge