In connection with futures contracts, it is a long position in a contract that is still not offset or closed. As of expiration, open long contracts would be expected to execute by receiving the underlying asset (e.g, shares of stock) and paying the price (and necessary amounts) to a brokerage account in order to cover the purchase of underlying asset.
For example, an investor who has purchased, or is long, 500 shares of XYX is said to have an open position in that share. The long position will still be open until the investor places an order to sell these shares and gets the the order filled by a market participant.
