There is an important difference between mass and weight.
Weight is the force of gravity on an object.
An object with a mass of one kilogram (1 kg) has a weight of 9.8 newtons (9.8 N).
You may already be familiar with kilograms -- these units are in common use in almost all of the rest of the world outside the United States. You may not be as familiar with units of newtons. We'll discuss newtons more in just a moment.