Mass: Mass is a fundamental universal property that gives a body inertia, or that is a measure of its inertia and the amount of matter it contains, giving the body a gravitational field of its own. So, we can say that mass is directly proportional to inertia, and the amount of matter a body contains; the more mass an object has, the more inertia it will embody. We should not confuse mass with weight, for weight is the pull of gravity. For example, a truck weighing 20 tons on the surface of the earth, out there in space free from the force of gravity, the truck will be weightless, but it will continue to have mass and inertia.
Inertia: Inertia is the property that a body has to maintain its state of motion, or rest, in which it finds itself. Inertia is directly proportional to mass and to the gravitational field a body has, that is to say, the more mass a body contains, the more inertia it deploys, and the stronger the gravitional field it will exert.