The anima or animus is a part of the psyche that is unconscious like the shadow. Unlike the shadow, which contains a series of archetypes denied that affect your behavior by erupting or projecting, the animus or anima is an image. The anima can be described as the (traditionally) feminine part of the male psyche. The animus is the (traditionally) masculine part of the female psyche. The anima is composed of the feminine qualities that men tend not to use or express a lot; for women, this is the same in reverse.
The famous Chinese yin/yang sign is a good example. The two side represent male and female. They narrow from wide to a single point to show that there is a wide range of how much male or female energy one has access to. But they each have a dot of the other inside
Whereas the shadow is highly individual, the anima or animus is biological and thus more universal. The animus or anima gets projected outward onto persons of the (usually) opposite sex but is closely related to who we choose as romantic partners. Whereas the shadow gets projected out as hate, the animus or anima gets projected out as love. The roles in romantic relationships are often projections of the traditional qualities associated with the opposite sex. A man may see a woman as seductress or saint. 
A woman may see her male lover as a hero or little boy. 
These may be precisely the roles that their inner opposites (anima and animus) would play for the individual. But because they are not lived out, they are projected outward.