Vishnu as the primordial being from which creation emanates, resting on the world serpent in the Milky Ocean, Kshira Sagara, the primordial sea.
The serpent has two names, Ananta – infinite and Shesha – leftover. From this ‚leftover‘ the new creation emerges.
Sheshasayana or Anantasayana is the resting place, sayana. The common translation is snake bed.