A memory is anything that happens and does not completely unhappen. The result is some trace which is left. The result may last for a long time or it may only last for a short time. Information that comes into the brain leaves a trace in the altered behaviour of the nerve cells that form the memory surface.
I’m not really interested in history. I’m interested in ideas. My approach to teaching is to show the evolution of ideas as opposed to the events that happened between 1955 and 1957. And that’s where the problem’s been. People want names and addresses and how much the guy weighs.