After seeing the question asked a few times, I decided to dig into it and provide everyone with an answer.
There are actually several meanings to the word Avatar – but only relates directly to the movie: (see below)
1. The incarnation of a Hindu deity, especially Vishnu, in human or animal form
2. An embodiment, as of a quality or concept; an archetype
3. A temporary manifestation or aspect of a continuing entity
But as it relates to the movie Avatar, here’s the meaning of Avatar that everyone is looking for:
As it relates to (Electronics & Computer Science / Computer Science) a movable image that represents a person in a virtual reality environment or in cyberspace.