In common parlance, mass is weight, but in science, mass is a measurement of an object's inertia, or resistance to acceleration. It can also be described as the degree to which an object bends space-time around it, according to the Theory of Relativity. One of the unsolved mysteries of physics is the origin of the rest-masses of the various particles. This origin is believed to be related to the Higgs boson, which is currently being sought in particle accelerators.
The scientific measure of weight is mass times acceleration due to gravity.