What is a Key Map?
A key map or key mapping is the association of keys or chords of the keyboard to specific actions, i.e. configuring what the keys do in a game, or customizing keyboard shortcuts of an application.
Why is Key Map called Key Map?
This comes from the term "map" in computing, which probably comes from "map" in mathematics. We call something a map if it "maps" i.e. "associates" values from one set of values to another set of values. In this case, we're "mapping" i.e. "associating" keys of the keyboard to operations that the program performs.