Mass is defined as the amount of matter that makes up an object. It is a measure of the quantity of matter in an object, typically measured in kilograms or grams.
To clarify the other options:
- Weight is the gravitational force acting on an object and is dependent on the mass and the acceleration due to gravity.
- The amount of force it takes to move an object relates to Newton's second law of motion (Force = Mass × Acceleration) and is not a direct definition of mass.
- The size of an object is more related to its dimensions or volume rather than its mass.
So the correct answer is "the amount of matter that makes up an object."