A special-purpose processing unit that assists the CPU in performing certain types of operations. For example, a math coprocessor performs mathematical computations, particularly floating-point operations. Math coprocessors are also called numeric and floating-point
Some computers come with coprocessors built in. For others, you can add a coprocessor. A math coprocessor can increase a computer's speed and power dramatically, particularly if you are running programs that perform a lot of floating-point arithmetic (engineering and scientific applications, statistical analysis, and graphics). Note, however, that the program itself must be written to take advantage of the coprocessor. If the program contains no coprocessor instructions, the coprocessor will never be utilized.
In addition to math coprocessors, there are also graphics coprocessors for manipulating graphic images. These are often called accelerator boards.