Amṛta(Amrita) is one of the thousand names of God Viṣṇu (Vishnu). To explain the meaning of this name, Śankarācārya (Sankaracharya), the commentator of Viṣṇusahasranāma (Vishnusahasranama), has said —
na vidyate mṛtaṃ maraṇamasyeti amṛtaḥ.
In Vṛhadāraṇyaka Upaniṣad, to explain the true manifestation of Brahman ( the Supreme Self), it is said — that Paramātmā is beyond ageing, death, he is amṛta (amrita; without death) and abhaya(without fear) -.
sa vā eṣa mahānaja ātmājaro’maro’mṛto’bhayo…
Philosophers have taken this word ‘Amṛta’ refers to someone who is beyond birth and death; and so he does not have the diseases or distortions that a mortal being is prone to. He is beyond all these. God Viṣṇu is identified as one with that conception of Brahman in Upaniṣad (Upanishad), so he is called Amṛta.