It is said that the mass of an object remains constant at all places,while its weight may change. Why?

(N/A) Mass is defined as the quantity of matter contained in an object and is an intrinsic property that remains constant regardless of location.
Weight is defined as the force with which an object is attracted towards the center of a planet or celestial body,calculated as $W = m \times g$,where $m$ is mass and $g$ is the acceleration due to gravity.
Since the value of $g$ varies from place to place (e.g.,it is different on the Earth's surface compared to the Moon),the weight of an object changes accordingly,even though its mass remains constant.