What is a CAD Drawing?

I recently saw the words cad drawing and I really have no idea what that means - does anyone know what a CAD drawing is?  I am always eager to learn, so any insight you could give me about this subject would be wonderful!  I try to read about many different subjects, and I consider myself to be a pretty knowledgeable person, but this is one thing I know absolutely nothing about.

Thanks for reading!  As always your participation in comments and discussions are encouraged and greatly appreciated!!