XNOR (Exclusive NOR) is the opposite of XOR (Exclusive OR)
A way to remember XOR is "must have one or the other but not both" XNOR is the opposite so it's "must have both or none" so both inputs must be 1 or 0.
XNOR or XOR is very common in homes with staircases so that you can turn on and off the light in the staircase regardless of which floor you are on.
If you google staircase switches, you will be told that they mostly use XOR but according to the wiring diagrams they use XNOR.