In generally when a person says "ANIMATION" it really means that he is telling or asking about the branch which a person have to study but, In practical, "ANIMATION" is a subject which contains the moving pictures or the illusion of moving pictures with a rapid display of sequence of images.

If you need a proper definition of Animation then you can write the below highlighted lines as a definition of animation

Animation: The word “ANIMATE” comes from the Latin verb “ANIMARE” means to make alive or to fill with breathe.
Animation is the rapid display of a sequence of images to create an illusion of movement. The most common method of presenting animation is as a motion picture or video program.
In simpler word animation means giving life to our imagination.