The original Enterprise, NCC-1701 is from the original series.
Enterprise from Star Trek Movies 1 through 3 would be considered the "Refit" as it was an upgraded version of the original ship, and was destroyed in Star Trek 3
Enterprise A is the ship seen at the very end of Star Trek 4, and subsequently in Star Trek 5 & 6, and was originally supposed to be the USS Yorktown, but was renamed Enterprise A, at least according to folk lore of Gene Roddenberry and the Star Trek universe.