Definition - What does Vishnu mean?
Vishnu, together with Brahma and Shiva, is one of the three deities of the Trimurti in Hinduism. He is the preserver and protector of creation.
Vishnu is most often represented as having four arms that hold four weapons: a padma ("lotus flower") in his lower left hand, a gada ("mace") in his lower right hand, a sankha ("conch") in his upper left hand, and the chakra (a discus weapon) in his upper right hand. According to the Hindu religion, the chakra is the most powerful weapon.
It's believed that in times when the balance between good and evil is destroyed and evil forces get the upper hand, the gods request that Vishnu incarnate himself in human form to set the balance right again. It's generally accepted that there have been 10 incarnations of Vishnu, though some sources cite more important Hindu figures as being his avatars.
In yoga, there's a pose dedicated to Vishnu. It's called sleeping Vishnu pose, or Anantasana.
Yogapedia explains Vishnu
Vishnu is seen as the divine arbitrator, who protects justice and moral order by interceding in all disagreements, whether they involve humans or gods. He is known for his patience and his gentle, merciful nature. Vishnu is associated with light - especially the sun.
In almost all Hindu denominations, Vishnu is either worshipped directly or in the form of one of his 10 avatars. The most famous of these avatars are Rama (the seventh) and Krishna (the eighth). Vishnu's wife and active energy is Lakshmi, the Hindu goddess of wealth, fortune and prosperity.
Vishnu is accepted as the main deity and Supreme Being by followers of Vaishnavism, and is also called Vasudeva, Hari, Kesava, Purusottama and Narayana. He is the god of time, space, life and joy. He brings great bliss to his devotees and the world. Vishnu is also the god of Karma yogis, the unselfish servants.
In yoga practice, sleeping Vishnu pose is performed by laying down on one side of the body, propped up on the elbow. Then the top leg is extended upwards with the arm as in reclining hand-to-big-toe pose.