The Sanskrit word avatāraḥ is derived from ava meaning ‘down’ or descent andtarati meaning ‘crossing over or tiding over’ and refers to the deliberate descent of a deity, immortal being or the Supreme Being from heaven (normally Viṣṇu) for specific purpose(s). As a noun, avatar also means a new personification of a familiar, idea¹ like an embodiment² or a temporary manifestation³.
God is one in Hinduism, to which there is no doubt and is represented by the sacred syllable om (ॐ).

¹ WordNet, Princeton University
² An embodiment, as of a quality or concept; an archetype: ‘the very avatar of cunning’. The American Heritage® Dictionary of the English Language, Fourth Edition; Dictionary.com
³ A temporary manifestation or aspect of a continuing entity: ‘occultism in its present avatar’. The American Heritage® Dictionary of the English Language, Fourth Edition;  Dictionary.com

• Avatāra - Mahāṛṣi Parāśara speaks of the dasa avatāra at the beginning of the work Bṛhat Parāśara Horā Śāstra and dedicated a whole chapter titled avatārakathana adhyāyaḥ to the study of the incarnations (avatāra) of Viṣṇu. Of the list of eleven avatāra, Parāśara omits Balarāma as, strictly speaking, Balarāma is an incarnation of Vāsuki, the divine serpent guardian of Viṣṇu. Table 2: Parāśara dasa avatāra Graha Sun Moon Mars Mercury Jupiter Avatāra Rāmacandra Kṛṣṇa Nṛsiṁha Buddha Vāmana Graha Venus Saturn Rāhu Ketu Lagna Avatāra Paraśurāma Kūrma Varāha Matsya Kalki Dasavatara PDF