What is the short answer of memory?

Can you explain to me what you consider memory to be—or rather, how do we remember?

Memory is, I consider, an impression made on the inner man through its brain organ. You will find that impressions made in your early youth are of a much more enduring character than those made recently. They appear to be deeply engraven on the young mind. Some persons say they have bad memories—the reason is not that the impressions are faint, but that in advanced life they get covered with rubbish and are not easily read by the spirit.

—Hafed, Prince of Persia. in Spirit