Alternate Universe – change in the canon
universe's timeline resulting in a different path/timeline from canon. (Time
stream that splits off from an actual past event and progresses in a different
manner from the base/original time stream/canon. ) *Example:
Canon until Harry sorts into Slytherin; or, Sirius doesn't die.
Alternate Reality – A reality transplanting
characters & places from canon; not set in the canon reality. (Reality/time
stream that runs concurrent (or parallel) to base/original time stream/canon.) *Example:
Canon characters and/or places (parallels), but no magic; or different
era-Harry is a WWII hero, and Snape is a German spy)