Computer Animation

Computer animation encompasses a variety of techniques, the unifying factor being that the animation is created digitally on a computer.

2D animation
2D animation figures are created and/or edited on the computer using 2D bitmap graphics or created and edited using 2D vector graphics. This includes automated computerized versions of traditional animation techniques such as of tweening, morphing, onion skinning and interpolated rotoscoping.
Examples: Foster's Home for Imaginary Friends, Danny Phantom, Waltz with Bashir
Analog computer animation
Flash animation
PowerPoint animation

3D animation
3D animation are digitally modeled and manipulated by an animator. In order to manipulate a mesh, it is given a digital skeletal structure that can be used to control the mesh. This process is called rigging. Various other techniques can be applied, such as mathematical functions (ex. gravity, particle simulations), simulated fur or hair, effects such as fire and water and the use of Motion capture to name but a few, these techniques fall under the category of 3d dynamics. Many 3D animations are very believable and are commonly used as Visual effects for recent movies.

Terms
Photo Realistic Animation, is used primarily for animation that attempts to resemble real life, Using advanced rendering that makes detailed skin, plants, water, fire, clouds, etc. to mimic real life. Examples include Up (2009, USA), Kung-Fu Panda, Ice Age (2002, USA).
Cel-shaded animation, is used to mimic traditional animation using CG software. Shading looked stark and less blending colors. Examples include, Skyland (2007, France), Appleseed (2007, Japan), The Legend of Zelda: Wind Waker (2002, Japan)
Motion capture, is used when live action actors wear special suits that allow computers to copy their movements into CG characters. Examples include Polar Express (2004, USA), Beowulf (2007), Disney's A Christmas Carol (2009 USA), Avatar (2009, USA).
2D animation techniques tend to focus on image manipulation while 3D techniques usually build virtual worlds in which characters and objects move and interact. 3D animation can create images that seem real to the viewer.