Plain English Meaning
A cockpit system that watches where the airplane is heading relative to the ground and surrounding obstacles, and warns the pilot — first with a caution, then with an urgent warning — if it looks like the airplane is about to fly into something.
Full Definition
An onboard avionics system that uses aircraft position, GPS data, and a stored database of terrain and obstacles to alert the pilot when the aircraft is at risk of unintentional contact with the ground or an obstacle. TAWS provides both cautionary alerts (giving time to assess and respond) and warning alerts (requiring immediate action), and is for most -powered configured with six or more seats.