What term describes a joint where no movement is possible?

The term that accurately describes a joint where no movement is possible is "immovable." Immovable joints, also known as synarthroses, are connected by fibrous tissue and do not allow for any significant movement between the bones they connect. An example of this type of joint would be the sutures found in the human skull, where the edges of the bones interlock and provide stability and protection for the brain.

The other terms do not align with the concept of a joint that permits no movement. While "flexible" implies a certain range of motion, it contrasts with the rigidity of immovable joints. "Mobile" suggests a high degree of movement, which is the opposite of an immovable joint. "Rotational" refers to joints that allow for rotary motion, like the shoulder or hip, further emphasizing movement, rather than a complete lack of it. Thus, "immovable" is the precise term that defines joints with no movement possible.