Flexibility relates to the range of movement possible at a joint, essentially how bendy you are. Many factors affect the range of movement possible, e.g. age, gender, genetics, the type and structure of the joint, but maximising flexibility can reduce the risk of injury, improve posture and improve everyday function. Stretching after a workout is important to help prevent muscle soreness a day or two later also stretching when the muscles are very warm will show the most benefit. It is dangerous to try to stretch cold muscles and you should only stretch to the point of tightness, not to where it causes discomfort. To get the most benefit it is recommended that you stretch 5-7 times a week, holding the stretch for 15-30 seconds.