Final answer:
The most movable muscular attachment is known as the muscle's insertion, which is contrasted with the origin attached to a fixed bone.
Step-by-step explanation:
When discussing muscular attachments, the term that refers to the most movable one is the muscle's insertion. During a muscle contraction, one end of the muscle, known as the origin, is attached to a fixed or stabilized bone. The other end, the insertion, is attached to the bone that is moved. An example of this is during forearm flexion, where the brachioradialis assists the brachialis muscle, with the brachialis acting as the prime mover and the brachioradialis as a synergist. Knowing the locations of muscle origins and insertions can greatly enhance understanding of muscle functions and the movements they produce.