ChristianAnswers.Net WebBible Encyclopedia
The expression “valley of Achor” probably became proverbial for that which caused trouble, and when Isaiah (Isa. 65:10) refers to it, he uses it in this sense: “The valley of Achor, a place for herds to lie down in;” i.e., that which had been a source of calamity would become a source of blessing.
Hosea also (Hos. 2:15) uses the expression in the same sense: “The valley of Achor for a door of hope;” i.e., trouble would be turned into joy, despair into hope. This valley has been identified with the Wady Kelt.