In Pixar's production process the term "TD" means Technical Artist. There are four main categories: Modeling & Rigging, Shading, Visual Effects, and Lighting.

Modeling & Rigging
The Modeling/Rigging TD will build either character or set models from concept artwork. Character Modelers rig and skin the models so that they can be animated. Set Modelers model the geometry of sets and props, as well as assemble these models into fully dressed sets. The modeler will construct shapes of the digital character or set in a 3D modeling software, such as Maya, then convert the models for use in our proprietary animation suite.
Shading
The Shading TD works alongside Modelers and Lighters to create the look of characters, sets, and other objects in the film. All textures and materials are developed by hand and must integrate into the Pixar worlds. The shading is created with RenderMan shaders, using a mixture of painted and procedural textures, along with sophisticated illumination models.
Visual Effects
The Visual Effects TD works to create visual effects in the animated film. Visual effects work often includes aspects of modeling, simulation, animation, shading, lighting, rendering and compositing for the visual effects elements of the shot. Visual effects work often includes simulation of dynamics and natural phenomena, as well as animation of effects elements either done by hand, or using procedural techniques.
Lighting
The Lighting TD creates the lighting of sets and characters in each shot of the animated film. Lighting makes the images look attractive, rich and interesting. It does this while conveying the mood, directing the viewer's attention to key story points, and ensuring that important actions are visible and easy to understand. A love of photography can be a great foundation for lighters. Lighting involves the placement and adjustment of lights in Pixar's lighting system, as well as the use of compositing tools to further enhance the appearance of the rendered image.

3D Layout Artists continue the visual story telling that has started in storyboarding. The tool that they use to tell the story is the CG camera. Akin to a cinematographer in film, 3D layout Artists create a sequence of shots with the use of camera composition, timing, and movements. These factors must guide the viewer's eye through the scene according to the Director's vision.

Animation is not merely moving an object. Animation brings the object to life and gives it a personality. The animator creates motions, gestures, and expressions of 3D characters and objects. Animators must know their character's motivation and back story, then use CG animation tools to "act" them out for the viewer.