Lets start with two dimension. two dimension is when the image or animation is flat and only has a height and a width but no depth.
Three dimension, in context to animation is when depth is applied to the width and hieght of the animation. this now becomes 3d.
Four dimension, gets more complicated and involes applying time to the animation or object.
and then you think it stops there but it dosn't.
six dimension is when you apply space to your animation.