Savasana
noun
Sa·va·sa·na shə-ˈvä-sə-nə 
variants or Shavasana or less commonly savasana or shavasana
yoga
: a meditative posture in which one lies on one's back that is typically considered the final resting pose in yoga
Savasana is a pose of total relaxation—making it one of the most challenging. 
Yoga Journal
Yoga Journalcalled also corpse pose
Word History
Etymology
borrowed from Sanskrit śavāsana-, from śávaḥ "corpse" (perhaps noun derivative from the base of śváyati "it swells, grows") + āsanam asana — more at cyme
First Known Use
1918, in the meaning defined above