A four card incomplete straight that can use a card on the high or low end to make it a five card straight. Ex. 4, 5, 6, 7 can use either a 3 or an 8 to complete the hand.
Also two way straight, or just open ender. A straight draw that can be completed by eight different cards. The hand 6789 needs either a five or ten. Open draws are twice as likely to hit as inside draws. Though much weaker, the hand 4-5-6 is an open ender of sorts, requiring either 2-3, 3-7, or 7-8. See runner-runner, also double inside straight draw. Open raise Both being the first to enter a pot preflop (excluding blinds), and entering with a raise, rather than just calling.