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 [Chapter 2] 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 […]