What is the definition of a socket joint?
A socket joint is a joint in which one bone has a ball-shaped end and fits into the cup-like socket or indentation of the adjoining bone, allowing movement in most directions and providing greater freedom of movement than other types of joints. It is also called a spheroidal joint and a ball and socket joint. In mammals the shoulder joint, where the humerus (upper arm bone) and scapula (shoulder blade) join, is an example of a ball and socket joint. The mammalian ankle and hip joints are also ball and socket joints. Other types of joints are hinge joints, such as the human knee and elbow, pivot joints, such as the neck and saddle joints found in knuckles. Below is a public domain image of a ball and socket joint: