(Or "trackpad") A stationary pointing device used mainly on laptop computers. Touchpads provide a small, flat surface that you slide your finger over using the same movements as you would a mouse. They were originally developed to provide a more natural and intuitive connection for the computer user than the mouse.
Touchpads use a principle called coupling capacitance, and requires a conductive pointer such as a finger. They contain a two-layer grid of electrodes which are connected to an integrated circuit (IC) mounted under the pad. The upper layer contains vertical electrode strips while the lower layer is composed of horizontal electrode strips. Capacitance from each of the horizontal electrodes to each of the vertical electrodes is measured by the IC. A finger near the intersection of two electrodes modifies the capacitance between them, since a finger has very different dielectric properties than air. The position of the finger is precisely determined based on these changes at various locations.