A flexible joint is a type of joint that allows for movement in multiple directions. The two most common types of flexible joints are the ELBOW and the HINGE. An ELBOW joint is a joint that bends and straightens, allowing for movement in two directions. A HINGE joint is a joint that allows for movement in one direction, usually up and down or side to side. Both of these types of joints are used in many different applications, from robotics to human anatomy.