His name means "that which remains", from the Sanskrit root sis, because when the world is destroyed at the end of the kalpa, Shesha remains as he is. So he is reffered as "Ananta-Shesha" which means "Endless Shesha". Lord Vishnu is seen resting on the coils of the serpent Shesha, also called Ananta.
A popular artistic rendering of Lord Vishnu (Adi Keshava) reclining on the serpent Ananta Sesha. Brahma can be seen atop the lotus issuing from Vishnu’s navel
An expansion of God who appears as a serpent with thousands of heads and who serves as the bed of Lord Vishnu. Ananta Sesha holds all the planets of the universe on His hoods and constantly sings the glories of Vishnu from all His mouths.
The fact that our true self resides in pure consciousness is also represented in the depiction of Vishnu. Vishnu is always shown residing in the ocean of milk, resting on Anantha Sesha. Vishnu is the true self, residing in the ocean of pure consciousness, and his resting on Anantha Sesha is representative of the fact that you know your true self by gaining mastery over the kundalini energy.