Mems are little ways of remembering things. You'll already know and use lots of them, without perhaps being aware of the fact: I'm talking about little phrases like "30 days has September, April, June and November".
Mems, I should of course note, are also known as mnemonics. Excellently, the word 'mnemonic' is so difficult to remember that it rather requires one of itself- a mnemonic- to help one remember it. Which is, let's face it, pretty silly. We much prefer the word 'mem'.
Mems are astoundingly effective for learning things: words, facts, relationships. Their effectiveness has been demonstrated empirically- and in two distinct ways. Through Science, in countless psychology experiments; but also through the interesting empirical device of the Memory Competition.
So psychology has demonstrated 3x increases in retention where mems are used to assist learning. But perhaps just as persuasively, and very interestingly, competitive memory competitions have also demonstrated the utter indispensability of the mem for the speediest of learning- and in a very original way.