The weight of
an object is the force of gravity on the object. This can differ
from place to place. The size of the force which gravity exerts
on a particular object. The same object on the moon's surface
would weigh only one-sixth of its weight on the earth, while in
an orbiting satellite it would be weightless.

The
SI unit of mass (and hence weight in some everyday senses) is the
kilogram. The SI unit of force (and hence weight in the mechanics
sense) is the newton (N) - which can also be expressed in
SI base units as kg m/s^{2} (kilograms times metres per
second squared).