What type of joints are described as synovial joints?

Synovial joints are characterized by their ability to allow considerable movement, which is why the correct answer describes them as such. These joints are unique in that they have a synovial cavity filled with fluid, which lubricates the joint and reduces friction during movement. The structure of synovial joints includes features like articular cartilage, a joint capsule, and ligaments, all of which contribute to their functionality and range of motion.

In contrast, the other types of joints mentioned in the options are classified differently based on their movement capabilities. Some joints allow only minimal movement, while others are designed to be immovable or only slightly movable. These limitations are due to the joint structures and the connective tissues involved, which are much more restrictive compared to the dynamic and flexible characteristics of synovial joints.