A rate of inclination; a slope. An ascending or descending part; an incline. Physics The rate at which a physical quantity, such as temperature or pressure, changes in response to changes in a given variable, especially distance. Mathematics A vector having coordinate components that are the partial derivatives of a function with respect to its variables. Biology A series of progressively increasing or decreasing differences in the growth rate, metabolism, or physiological activity of a cell, organ, or organism.