What is Weight and Mass?

In short

Mass is the amount of matter in an object, in kilograms. Weight is the force of gravity on it, $W = mg$ , in newtons.

In simple words

Mass does not change from place to place, but weight does, because $g$ does. An astronaut has the same mass on the Moon as on Earth, but about one sixth of the weight. In deep space, far from any gravity, the weight is nearly zero, and the mass is the same. A force is still needed to change the speed of a mass, because of its inertia.

Example

A rover has a mass of $185\ \text{kg}$ . Its weight on Earth is $185\ \text{kg} \times 9.80\ \text{m/s}^2 = 1813\ \text{N}$ . Far from gravity its weight is almost zero, but its mass is still $185\ \text{kg}$ .