The name is generally considered to be of Welsh origin (though an Old Cornish or Old Breton origin is also possible), derived from Old Welsh, Old Cornish, or Old Breton aball or avallen(n), “apple tree, fruit tree” (cf. afal in Modern Welsh, derived from Common Celtic *abalnā, literally “fruit-bearing (thing)”). It is also possible that the tradition of an “apple” island among the British was related to Irish legends concerning the otherworld island home of Manannán mac Lir and Lugh, Emain Ablach (also the Old Irish poetic name for the Isle of Man), where Ablach means “Having Apple Trees”—derived from Old Irish aball (“apple”)—and is similar to the Middle Welsh name Afallach, which was used to replace the name Avalon in medieval Welsh translations of French and Latin Arthurian tales. All are etymologically related to the Gaulish root *aballo “fruit tree”—(as found in the place name Aballo/Aballone) and are derived from a Common Celtic *abal- “apple”, which is related at the Proto-Indo-European level to English apple, Russian яблоко (jabloko), Latvian ābele, et al.
Source: Avalon – Wikipedia