A Low Dropout Regulator (LDO) is a type of linear voltage regulator that can regulate an output voltage even when the input voltage is very close to the output voltage. The key characteristic of an LDO regulator is its low dropout voltage, which is the minimum difference between the input and output voltage required for the regulator to maintain proper regulation. LDOs are widely used in battery-powered devices, low-voltage circuits, and applications where power efficiency and small voltage differences between input and output are crucial.