An avatar is composited by graphics and animation.
The avatar graphics are its looks. It is not a static image but a collection of images to display the directions and appearance. There are different approaches of drawing the avatar graphics depending on the render methods and how many directions and animations the avatar needs.
Animations represent different actions of the avatar. The most basic animation is walking. Other animations such as hand waving and throwing objects are also common. There will be different animation sets for different virtual world designs. A fighting topic virtual world will probably contain a collection of fighting animation sets. A hunting topic virtual world will contain animations of collection items and using hunting tools.