the gradient of the temperature field; the rate of change of temperature over some distance in a given direction, usually horizontally or vertically
The rate of change in temperature, which can be expressed in terms of change per unit of distance or per unit of time.
In atmospheric sciences (meteorology, climatology and related fields), the temperature gradient (typically of air, more generally of any fluid) is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location. The temperature gradient is a dimensional quantity expressed in units of degrees (on a particular temperature scale) per unit length. The SI unit is kelvin per metre (K/m).