LDO (low-dropout regulator)
also known as: Linear regulator
A linear regulator that holds its output voltage by burning the difference as heat — continuously adjusting a pass transistor so Vout stays put. 'Low-dropout' means it keeps regulating even when Vin is only a few hundred millivolts above Vout.
In practice
Heat is (Vin − Vout) × Iout, full stop. Dropping 12 V to 3.3 V at 500 mA is 4.35 W of heat — that's a switcher's job. LDOs shine for the quiet final volt: clean, simple, no switching noise, perfect after a buck has done the heavy lifting.