The concepts of mass and weight are often confused. The mass of an object, most often expressed in kilograms (kg), refers to the amount of stuff present in the object. More stuff (atoms) and more massive stuff (more massive elements) means the object possesses more mass. This mass value is not location dependent. A 2-kg textbook on the Earth would still possess a mass of 2 kg when it is brought to the moon.
The weight of an object is quite different. Weight refers to the force with which gravity pulls downward upon the stuff in the object. Weight is the gravitational force of attraction to the Earth (or to whatever massive body the object is on). Because weight is a force, it's standard unit is the Newton (N). And because it is a force of gravity, its value is dependent upon the gravitational environment where it is located. As such, the weight of an object varies with location. A 2-kg textbook would weigh approximately 20 N on Earth; but when brought to the moon, it's weight would be less than 4 N. The weight of an object can be calculated by multiplying the mass of an object by "g". This g value is known as the gravitational field strength (often referred to as the acceleration of gravity).