What does the word 'myoelectric' mean?
Myoelectric refers to one type of prosthetic arm. The action of the arm, for example, the opening or closing of the hand is controlled by the flexion of muscles in the residuum.
Electrodes (usually 2) are strategically placed in the wall of the prosthetic socket. The electrode is placed directly over a muscle, when that particular muscle is flexed, the electrode picks up the signal. As a result, for example, the hand will open.
This is a very simple explanation of myoelectric as it applies to prosthetics.