2D animation is motion that takes place within a flat, two-dimensional space. 3D animation adds the concept of depth. This means that 2D animation can often be created more easily than 3D, using less technical and specialized tools. For example, you do not need to create 3D models in order to create a simple 2D animation. Instead, you can simply draw your characters or objects on a flat surface and then animate them by manipulating the individual frames of your animation.
Find out more about the differences between 2D and 3D animation.