EGPWS / TAWS
Terrain awareness and warning systems. They compare the aircraft's position against a terrain database and call "terrain, pull up" before impact.
The original GPWS used the radio altimeter and reacted to closure with the ground beneath the aircraft. The enhanced version adds a worldwide terrain database and GPS position, so it can warn about terrain ahead rather than only underneath, which is what gives the crew enough time.
Mandating these systems is the single largest reason CFIT rates collapsed in commercial aviation, and reports still examine whether the warning sounded and whether the crew's response was immediate and full.
Related terms
An airworthy aircraft, under the crew's control, is flown into ground, water or an obstacle, usually because nobody on the flight deck knew the terrain was there.
Airborne collision avoidance. It interrogates nearby transponders and, if a collision is likely, issues a coordinated climb or descend instruction to both crews.