RAFRAF As the name suggests, it signals idle status. When your Mac is in idle (e.g., no input from users) the LED is OFF. When you are doing something with your Mac the LED is ON.
The word LED is ok, but IdleLed is the own name on the App... so the stuff LED and led doesn't matter. In the docs I think that the word LED has been correctly spelled (i hope).
(Version 1.0)