Savasana
śavāsanaCorpse pose: the final rest at the end of class. Genuinely ancient, unlike much of what precedes it.
The rest at the end of practice is not a modern indulgence. The Hatha Yoga Pradipika describes it, names it, and prescribes it:
Lying down on the ground, like a corpse, is called Śava-âsana. It removes fatigue and gives rest to the mind.
The original Sanskrit
uttānaṃ śabavad bhūmau śayanaṃ tac chavāsanam / śavāsanaṃ śrānti-haraṃ citta-viśrānti-kārakam
Lie down like a corpse; it removes fatigue and rests the mind. Five centuries later, that is still exactly the instruction.