Uncertainty: A parameter, associated with the result of a measurement that characterizes the dispersion of the values that could reasonably be attributed to the measured.

Unit: A value, quantity, or magnitude of which other values, quantities, or magnitudes are expressed.

Vacuum: Any pressure below atmospheric.

Velocity: The time rate of change of position.

Velocity Constant: The ratio of the velocity of propagation in a transmission line to the velocity of light.

Viscosity: Resistance of a liquid to sheer forces (and hence to flow).

VSLI: Very Large Scale Integration.

Volatile: Readily vaporizable at a relatively low temperature.

Volume: The amount of space which matter occupies.

Wave Front: A surface composed at any instant of all the points just reached by a vibration disturbance in its propagation through a medium.

Weight: The force of gravity acting on an object.