Another “celestial barge”, this one from the final scene of Excalibur (1981). © Orion Pictures Company.
I’ll quote here Wikipedia’s etymology section on this word:
Geoffrey of Monmouth referred to it in Latin as Insula Avallonis in the Historia. In the later Vita Merlini he called it Insula Pomorum the “isle of fruit trees” (from Latin pōmus “fruit tree”). The name is generally considered to be of Welsh origin (though an Old Cornish or Old Breton origin is also possible), derived from Old Welshaball, “apple/fruit tree” (in later Middle Welsh spelled avall; now Modern Welshafall). In Breton, apple is spelled “aval”/ “avaloù” in plural. It is also possible that the tradition of an “apple” island among the British was influenced by 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- (as found in the place name Aballo/Aballone, now Avallon in Burgundy or in the Italian surname Avallone) 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.
It makes sense, then to point to the Atlas and the Hesperides post, where there is some elaboration on the apple tree subject.