Most of the major muscle groups used or movement and communication are voluntary. Involuntary muscles would be things like your heart and the muscles around your intestines, which you generally cannot consciously control. The skeletal is called voluntary muscle because it is usually subject to conscious control.
Medical Definition of Autonomic nervous system. Autonomic nervous system: A part of the nervous system that regulates key involuntary functions of the body, including the activity of the heart muscle; the smooth muscles, including the muscles of the intestinal tract; and the glands.
Medical Definition of Parasympathetic nervous system. Parasympathetic nervous system: The part of the involuntary nervous system that serves to slow the heart rate, increase intestinal and glandular activity, and relax the sphincter muscles. The parasympathetic nervous system, together with the sympathetic nervous system, constitutes the autonomic nervous system.