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Vishnu (; Sanskrit: विष्णु, IAST: "") is one of the principal deities of Hinduism, and the Supreme Being in its Vaishnavism tradition. Vishnu is the "preserver" in the Hindu trinity (Trimurti) that includes Brahma and Shiva. 

In Vaishnavism, Vishnu is identical to the formless metaphysical concept called Brahman, the supreme, the Svayam Bhagavan, who takes various avatars as "the preserver, protector" whenever the world is threatened with evil, chaos, and destructive forces. His avatars most notably include Rama in the "Ramayana" and Krishna in the "Mahabharata". He is also known as Narayana, Jagannath, Vasudeva, Vithoba, and Hari. He is one of the five equivalent deities worshipped in Panchayatana puja of the Smarta Tradition of Hinduism. 

In Hindu inconography, Vishnu is usually depicted as having a dark, or pale blue complexion and having four arms. He holds a padma (lotus flower) in his lower left hand, Kaumodaki gada (mace) in his lower right hand, Panchajanya shankha (conch) in his upper left hand and the Sudarshana Chakra (discus) in his upper right hand. A traditional depiction is Vishnu reclining on the coils of the serpent Shesha, accompanied by his consort Lakshmi, as he "dreams the universe into reality". 

Yaska, the mid 1st-millennium BCE Vedanga scholar, in his Nirukta (etymological interpretation), defines Vishnu as "viṣṇur viṣvater vā vyaśnoter vā", "one who enters everywhere". He also writes, "atha yad viṣito bhavati tad viṣnurbhavati", "that which is free from fetters and bondages is Vishnu". (End of story)

Provide your best guess for the following question. Give ONLY the guess, no other words or explanation.

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Guess: <most likely guess, as short as possible; not a complete sentence, just the guess!>

Here are a few examples of questions and answers:

Question: What religion is focused on?
Guess: Hinduism

Now answer the following question in the same format.

Question: What is Vishnu?

"preserver" in the Hindu trinity