Flexibility is generally defined as the range of motion of the joints. It is the ability to bend and stretch easily without too much effort. Flexibility depends upon various factors like the state of the joints, muscles, length and looseness of muscles, shape of bones, age etc. Some medical conditions like arthritis can affect flexibility.
This flexibility can be attained by effective exercise and also through yoga. Stretching is generally done to increase flexibility. Flexibility can be best gained by performing stretching exercises which may include exercises of back, neck, shoulder, wrist, legs etc. If exercise is done in a proper way it is observed that a person with a rigid body before starting exercise will have gained flexibility of almost every part of his body with regular practice of exercise.
This how to video demonstrates a variety of poses that help increase your flexibility.