A map (or dictionary) is an key-value lookup. Like a word dictionary. Given a key we look up a value. A key is associated with a value.
JavaScript has an old way of doing maps (using "plain objects") and a new "Map" type.
The old way is very much in play (and a lot of code and sources out there use it), so we'll want to learn it first.
Here is some food to feed into our labs:
JavaScript Guide
(Chapter 406 - Map)