Well, I see two meanings of the word.
The first, the more general term being one of the six scientific groupings of life (Animalia, Plantae, Fungi, Protista, Archaea, and Eubacteria).
The second could refer to the slightly more colloquial non-human, living, breathing organism.
So, when animal is used in a biological context, humans are included. When it is not used in a biological context, humans are generally not included.
I would like to give special thanks to Webster's for helping us clear this all up.