Joints are necessary for proper mobility. Joint bones (combined with muscles, ligaments and tendons) work alongside one another to provide specific ranges of motion for limbs or other major portions of the body. The bones also have unique shapes that complement one another, providing optimal protection and support. In this article, the major joints of the body, known as synovial joints (freely moving), and their different categories are explained. Synovia is the white lubricating fluid secreted inside these joints to keep them operating smoothly.