NOT gate (also often called Inverter) is a logic gate. It takes one input signal. In logic, there are usually two states, 0 and 1. The gate therefore sends 1 as output, if it receves 0 as input. Alternatively it received 1 as input, and sends 0 as output. usually this gate can be in combination to other logic gates.
Symbols of NOT gate
There are three symbols for the NOT gate: