Final answer:
Among the options provided, 'Syndesmosis' does not represent a functional classification of joints; it is actually a type of joint within the amphiarthrosis category, which allows slight movement.
Step-by-step explanation:
The functional classifications of joints are synarthroses, amphiarthroses, and diarthroses. Synarthroses are immovable joints and include sutures, gomphoses, and synchondroses. Amphiarthroses are joints that allow slight movement and include syndesmoses and symphyses. Finally, diarthroses are joints that allow for free movement, which are exemplified by synovial joints. Based on this classification, the correct answer is D. Syndesmosis, as it is not a functional classification of joints but rather a type of amphiarthrosis.