The mass of a thin layer of uniform thickness added to or subtracted from a reference model of the solid and liquid Earth over a specified region, particularly a glacierized region, during a specified period. See GRACE, gravimetric method. Mascon is an abbreviation by geodesists of 'mass concentration', coined originally to stand for a large positive gravitational anomaly. In modern usage the mascon itself is a number representing the mass of the layer as a surface density (kg m-2), although the word is often used loosely to refer to the 'mascon region', that is, the region over which the mass is added or subtracted. The 'mascon parameters' are sets of coefficients describing the difference of gravitational potential that arises due to the mascon.