The mass of an object is the 'amount of matter it contains'. The mass of an object stays constant if you move it. Mass measures the resistance of a body to a force, and is equal to the ratio of the applied force to the acceleration the mass experiences as a result of the applied force.
\[Mass =\frac{Force}{Acceleration}\]
or \[m=\frac{F}{m}\]
This is commonly written as
\[F=ma\]
and is known as Newton's Second Law.The weight of a body is a very different concept from mass. A body only has a weight because it is in the gravitational field of another body. Thing on the Earth experience the Earth' gravity. Everything on the Earth experiences a force towards the centre of the Earth of 9.8 Newtons for every kilogram of mass.
For this reason we can write the weight of a body on the Earth as
\[W=mg\]
where \[g=9,8 m/s^2\]
.In the absence of a gravitational field, a body is weightless, even though the mass is the same as if it were in a field eg on Earth.