Final answer:
Freely movable joints found at the ends of long bones are called synovial joints, which include features like a synovial cavity filled with fluid and articular cartilage to facilitate movement and reduce friction.
Step-by-step explanation:
The freely movable joints typically found at the end of long bones are known as synovial joints. Synovial joints have a distinctive space between the adjoining bones called the synovial cavity, which is filled with synovial fluid. This fluid acts as a lubricant, reducing friction and allowing for a wide range of movement. Articular cartilage covers the surfaces of the bones, and the entire synovial joint is encapsulated by an articular capsule, which is made of connective tissue. The capsule not only permits movement but also resists dislocation, and it may include ligaments that further stabilize the joint. These joints are the most common and allow for various types of movements such as angular and rotational.
Movable joints like the knee, elbow, and shoulder are all examples of synovial joints, which are characterized by features that facilitate movement while maintaining stability. Ligaments often cross these joints, holding the bones together and providing additional support. For the final answer, synovial joints are the option that corresponds to freely movable joints at the end of long bones, as described in the question.