Rectification is the process by which alternating current, which reverses direction periodically, is transformed into direct current, which always flows in the same direction.

Full wave rectifier:

During the positive half cycle, the terminal closest to diode D1 is positively charged. Due to this, only the diode D1 conducts since its p side is connected to the positive terminal (forward biased). The diode D2 does not conduct since its p side is connected to the negative terminal (reverse biased). Hence, current flows in the clockwise direction from D1 to the resistance R.

During the negative half cycle, the terminal close to diode D2 becomes positively charged. So, only D2 is in forward bias and conducts current, flowing in the anticlockwise direction to the resistance R.

Hence, the flow of current through resistance R becomes unidirectional. This is called rectification.

Before rectification:

After rectification: