The corpse pose is practiced at the end of the 12 basic Asanas (postures) as taught by Swami Vishnu-devananda , founder of the Sivananda Yoga Vedanta Centers.

Definition: The Yogic Posture for Deep Relaxation

Lying flat on your back, bring the feet at least 1 1/2 feet (50 centimetres) apart, and allow the toes to fall outward to the sides.
Place the arms at an angle of approximately 45 degrees to the body.
Relax the hands, allowing the fingers to curl gently.
Make your breathing very gentle and regular.

The relaxation process

Raise the different parts of the body and contract them very hard for 5 to 6 seconds, then release and relax.
Starting with the legs, do the same for arms, hips, chest and shoulders. Finally contract the facial muscles as well.

• Beginning with the toes, feel as though a wave of relaxation is slowly moving up through the entire body.
  Mentally relax each toe, and then move on to the feet. Relax them completely.
• Feel the relaxation moving up the legs, relaxing the calves, the knees, and the thighs.
  Feel the relaxation coming up into the hips and the abdominal region.
  Relax all the internal organs.
• Relax the buttocks and feel the tension slowly releasing from each part of the back.
  Allow the floor to hold you up and, as the body relaxes, feel as though you are sinking down into it.
• Feel the relaxation coming into the chest, breathing very slowly and gently.
• Bring your attention to the fingers, relaxing each one in turn.
  Then relax the hands. Feel the relaxation moving up the arms, relaxing the wrists, forearms, and then the upper arms.
• Allow the shoulders to relax.
  Feel the wave of relaxation moving up the neck into the head.
• Relax the face and head. Begin with the jaw and let the mouth hang open slightly.
  Relax the tongue and the muscles at the back of the throat.
  Relax the chin and the cheeks, then the eyes and eyebrows, the forehead, and the scalp.
• Finally, relax the brain. All cares and worries are gone.
  Allow the mind and body to remain in this state of relaxation for at least 5 minutes more.