What are joints in the human body?

Joints in the human body are structures where two or more bones are connected, allowing for movement and stability. They play a critical role in the functionality of the skeletal system by providing flexibility and enabling various types of motion, including bending, twisting, and rotating. The ability of joints to facilitate movement is essential for everyday activities, exercise, and overall physical fitness.

In the context of the options provided, the other choices do not accurately describe the nature of joints. A space in the digestive system pertains to the gastrointestinal tract, which is unrelated to skeletal function. A type of muscle group refers to the clusters of muscles that work together to produce movement, which is separate from the structural connection made by joints. A fluid-filled cavity does not encapsulate the full definition of a joint, as it may refer to various anatomical features but does not specifically denote the connection between bones.