If you weigh 150 lb (68 kg) on the Earth, you would weigh only 25 lb (11 kg) on the Moon.
Weight is the force gravity exerts on an object due to its mass. Mass, roughly, measures an object's inertia, its resistance to being moved or stopped, once it's in motion. Your mass remains constant across the universe (except in certain cases discussed in special relativity, but that is another story), while your weight changes depending on the gravitational forces acting on you, which vary from planet to planet.
Newton's Law of Universal Gravitation says that everything that has mass attracts every other thing that has mass, pulling with a force (a) directly proportional to the product of the two objects' masses and (b) inversely proportional to the square of the distance separating their centers.
In other words, although gravity increases linearly as objects grow more massive, it decreases exponentially as the distance between them increases (a phenomenon known as an inverse-square law). When calculating surface gravity, that distance refers to the space separating you (on the surface) from the planet's center of mass. This means that a planet's size actually has a greater relative impact on its gravity and on your weight on its surface than does its mass.