Which type of joint is best described as immovable?

The type of joint described as immovable is synarthrosis. This classification of joints is characterized by the absence of movement, with the bones being closely connected by fibrous tissue or cartilage. Examples of synarthrotic joints include the sutures of the skull, where the edges of the bones are tightly fused together to provide stability and protection for the brain.

In contrast, the other types of joints allow for varying degrees of movement. Amphiarthrosis, for instance, permits slight movement, often found in joints like the pubic symphysis. Diarthrosis refers to freely movable joints, such as the knee or shoulder, which allow for a wide range of motion. Cartilaginous joints can also allow some movement but not to the extent seen in diarthrosis; these joints are primarily connected by cartilage, as seen in the intervertebral discs of the spine.

Understanding these distinctions highlights why synarthrosis is specifically referred to as an immovable joint type, making it the correct choice.