The document discusses the skeletal system's joints. It begins by defining joints as the points where bones meet, allowing movement. It then categorizes joints based on structure and mobility. The main joint types discussed are fibrous, cartilaginous, and synovial joints. Synovial joints are the most common and complex, with features like articular cartilage, joint cavities, and ligaments. The document outlines six synovial joint types - ball and socket, condyloid, gliding, hinge, pivot, and saddle - along with the movements each permits. It concludes by discussing joint problems like sprains, dislocations, bursitis, osteoarthritis, rheumatoid arthritis, and gout.