A rectifier is a circuit or device that converts alternating current into direct current. It is a key part of many power supplies and chargers.
How rectifiers use diodes
Rectifiers commonly use diodes, because diodes allow current to flow mainly in one direction. A bridge rectifier uses four diodes to make better use of both halves of an AC wave.
What happens after rectification
The output of a rectifier may still be uneven or pulsing. Capacitors and voltage regulators are often used afterward to smooth and stabilize the DC voltage.
In short, a rectifier is the circuit that helps turn wall-style AC into electronics-friendly DC.