Flex on a golf club refers to the amount of bend the shaft can handle, and the give you need will depend on the type of swing you have. Ideally, a player with a strong swing speed should be looking at a less flexible shaft so they can keep control of the ball off the face of the club, while a player with an average swing speed needs something with a little more flexibility. Flex can vary from manufacturer to manufacturer, but the golf fairway woods you choose should be flexible enough to provide the distance and accuracy you need, while staying in control.