Why is a flip-flop also known as a latch?
Because the electronic device reminded engineers of both this item:

and this one:


In the first case, the devices have two states: flipped (in contact with heel) and flopped (not in contact with heel). In normal use they alternate continuously between those two states at about 1Hz.

In the latter case, you can change the object's state from open (unlatched) to closed (latched) by pushing the device. Once in the second state it cannot be returned to the first state by more pushing, you have to apply a specific reset operation to go from closed (latched) to open (unlatched).