Question

Why is a NOT gate known as an inverter?

Answer 1

The not gate or Inverter: It is a circuit with one input whose output is high if the input is low and vice versa. The not operation outputs an inverted version of the input. Hence, a not gate is also known as an inverter.
The small invert bubble on the output side of the inverter logic symbol, the following figure, and the over bar (¯¯) in the Boolean expression represent the invert function.

Logic symbol:

Boolean expression: Y = `bar"A"`

Truth table:

Input A	Output Y
0	1
1	0