This is a type of Mnemonic Peg System that helps you memorize lists using a pre-built Peg List based on the alphabet. It doesn't have to be the alphabet, it can be any ordered list of words that you already have memorized.
First you created a list of words wherein the first letter of each word matches the letters of the alphabet - Ape, Bat, Crane, etc. Now whenever you need to memorize a list you associate each item on the list with a word in the alphabet list in order. So if you need to memorize a loaf of bread, a container of milk, and a stick of butter you would do something like this:
|Ape||Loaf of Bread||King Kong climbing the Empire State Building holding a loaf of bread|
|Bat||Container of Milk||Supermarket milk jug with a bat in it|
|Crane||Stick of Butter||A crane choking on a giant stick of butter|
Once you've made the associations you can remember the list by starting with Ape and working through the alphabet.