3D Rendering is a process of wherein 3D wire frame models are automatically converted to 2D images. This is usually done with 3D photorealistic or in some cases non-realistic rendering on a computer. Rendering is the final process of creating the animation from the prepared scene. The process might take fraction of a second or days for a single image/frame because the computer is photographing each pixel of the image, calculating color of each pixel, tracing light rays around the 3D scene and this means a lot of calculations. To render a whole movie might take hundreds of computer working together for months or years.
Even though it is called “3D”, it does not mean it will create a depth of field when you wear 3D glasses. It is called “3D” because of the way they are made. 2D images have 2 axis but the third axis in 3D creates the depth in the character to make it feel realistic and giving it a 360-degree view. The final product on cheap 3D rendering is a normal two-dimensional image. 3D rendering is a creative process similar to photography where you add lights and extra effects to produce images. The difference is just that 3D rendering is done in computer and photography in real. The scene in the computer is created using Modeling and Animation before Rendering can be done.