CAD stands for Computer-Aided Design.
CAD is the use of computers and software to create, modify, analyse or optimise design. The so called CAD software is the program to perform the design tasks and helps to improve the productivity of the designer and the quality of the design itself.
The output is usually a electronic file format which can be used for printing, manufacturing or further analysis.
Today, there exists a wide market for CAD software and systems. Often the CAD applications are in some way specialised for a certain type of design.