The island to which Britain's legendary King Arthur was conveyed for the healing of his wounds after his final battle. It was ruled by the enchantress Morgan le Fay and her eight sisters, all of them skilled in the healing arts.
Van Morrison often uses Avalon as a metaphor in his songs for any idyllic place of healing. "Healing" is a big issue with Van Morrison, as is "crossing over" for Joe Henry. It may be one in the same thing.