To define and to understand the anima archetype, I went straight to the source. CG Jung, in Memories, Dreams, Reflections, states that the anima is an "inner feminine figure (that) plays a typical, or archetypal role in the unconscious of a man" with both negative and positive aspects. The negative anima aspect is "full of deep cunning". The positive role the anima plays is described by Jung as "she who communicates the images of the unconscious to the conscious mind".
(see Bibliography Category for sources)