Rare literary term for the farthest edge or limit of something, often used in abstract or poetic contexts. Modern Japanese more commonly uses 限界 or 果て.
The poet gazed at the limits of the sea.
Compound of 際 (edge, verge) and 涯 (horizon, limit). The exact historical derivation is uncertain, but it is a Sino-Japanese word (kango) with a literary feel.