Quoted from killerrobots:... NOT gate
Software background. Logical operator. In C/C++ symbolized as "!".
Quoted from GRUMPY:My whole life I have called this a buffer/amplifier. U-55 is a inverting amplifier.
Hardware background. A whole slew of different types of silicon (open collector, schmitt trigger, CMOS, TTL). Not to mention fanout. Inverts low level logic to high level logic or visa versa.