The mass refers to the property of the object while weight refers to the force of gravity on a given object.

-quote-

" The mass of an object is a fundamental property of the object; a numerical measure of its inertia; a fundamental measure of the amount of matter in the object. Definitions of mass often seem circular because it is such a fundamental quantity that it is hard to define in terms of something else. All mechanical quantities can be defined in terms of mass, length, and time. The usual symbol for mass is m and its SI unit is the kilogram. While the mass is normally considered to be an unchanging property of an object, at speeds approaching the speed of light one must consider the increase in the relativistic mass.

The weight of an object is the force of gravity on the object and may be defined as the mass times the acceleration of gravity, w = mg. Since the weight is a force, its SI unit is the newton. Density is mass/volume. "

-end of quote-
Source(s):
http://hyperphysics.phy-astr.gsu.edu/hbase/mass.html

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Mass has not yet been absolutely defined, in that we still don't know its source. We know that mass is a measure of inertia, i.e. the tendency of an object to continue its motion (or lack thereof) unless an external force is applied to it.

We also know that mass is the basis of interaction with a gravitational field (with a bit of a caveat in that relativity allows mass-less particles such as photons to be "lensed" by strong gravitational fields due to distortion of the local space metric).

There is a hypothesized Higgs boson (or set of such, depending on the theory you like) which interacts with other particles, with an interaction strength related to a particle's mass. This has been touted as a possible explanation to the source of mass, though it appears all that does is replace mass as an unexplained number with the interaction constant with the Higgs field as the unexplained number.

Weight "w" is simply a special word we've given to the force gravity exerts on an object. On Earth, that force is equal to the product of an object's mass "m" by the local gravitational acceleration "g" (approximately 9.81 m/s^2), i.e.:

w = m*g.

While we usually quote weight in lbs or kg, technically speaking, these are "force-pounds" and "force kg" since lbs and kg measure mass, not weight. In the internationally accepted SI (Systeme Internationale, and expansion of the metric system) units system, weight, like other forces, is measured in Newtons (symbol N), where 1 N = 1 kg * 1 m/s^2.
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Mass is the amount of matter in an object and is measured in kilograms.
Mass is not a force and has the same value anywhere in the Universe, including outer space.
Weight is a force and is caused by the pull of gravity acting on a mass. Like other forces, weight is measured in newtons and has both magnitude and direction.
Weight has different values depending on where the object is in the Universe.
Source(s):
http://www.examville.com

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