Voici l'explication (en anglais ! i'm sorry et surtout trop paresseux pour traduire ! sauf si tu le désire)
AE Abbreviation for Aeratus, Latin for copper. In numismatics, the term is used to describe a coin whose given name is unknown or whose denomination is unclear due to poor preservation. Generally speaking, for Roman coins there exist four categories:
AE1: Copper coins (to include bronze, billon, orichalcum, etc.) of size over approximately 27mm in diameter.
AE2: Coins ranging in size from ~22mm to ~27mm in diameter.
AE3: Coins ranging in size from ~16mm to ~21mm in diameter.
AE4: Coins smaller than about 16mm in diameter.