A NOT gate is a basic digital logic gate that performs a simple operation: it inverts its input. If the input is a high signal (1), the output will be a low signal (0), and vice versa. This means that the NOT gate always produces the opposite value of what it receives. It is often represented by a triangle pointing to the right with a small circle at the output.
NOT gates are fundamental components in digital circuits and are used in various applications, including computer systems and microcontrollers. They help in creating more complex logic functions when combined with other gates like AND gates and OR gates.