A working order is a general term for either a stop or limit order to open. It is used to advise your broker to execute a trade when an asset reaches a specific price.
Working orders are one of several varieties of orders, including market orders that will execute at the best available price that day, or good-‘til-cancelled orders that remain open indefinitely.
Unlike most types of order, though, working orders are not differentiated by their expiry date. Instead, working orders can have any length of expiry attached to them, from the same day to good-‘til-cancelled.