In atmospheric sciences (meteorology, climatology and related fields), the<unk> (typically of air, more generally of any fluid) is a physical quantity that describes in which direction and at what rate the<unk>  changes the most rapidly around a particular location. The<unk> is a dimensional quantity expressed in units of<unk>  per unit length. The SI unit is pascal per metre (Pa/m).
Pressure gradient 
Volumetric flow rate
Electrochemical gradient
Density
A-a gradient
Fluency
Blood flow
Moment of inertia