A varactor diode, also known as a varicap diode, is used in the TV tuner stage of a TV receiver. It acts as a voltage-controlled capacitor and is commonly used in electronic tuning circuits.
In the tuner section, the varactor diode helps in selecting different channels by varying its capacitance according to the applied tuning voltage. This changes the resonant frequency of the tuner circuit, enabling the receiver to lock onto different broadcasting frequencies.