An avatar, similar to the Christian concept of the incarnation of God, is different in two ways. Firstly, a god can incarnate in many places at the same time through "partial" avatars, called amshas, but the main from remains entirely “full". Secondly, the incarnations do not completely participate in the human sufferings and also lose the power and knowledge of their divine form.
The term 'Vatar' symbolizes the one who has descended. It means that he descended from his godly state to the human form. So, Avatar means the beings who descended from the Spiritual World to the Earth to establish Dharma, preserve the human race and promulgate Sastra. Thus, Avatar means the form who descends as a partially or fully-empowered incarnation of the Divine Mother, Adhiparasakthi.