The theoretical wind generated when pressure gradient forces are exactly balanced by the Coriolis force. Most atmospheric motions are not geostrophic, due to frictional and other effects.
The calculated or measured wind that occurs when the pressure gradient acceleration equals the Coriolis acceleration. The geostrophic wind is seen above the boundary layer, in the upper layers of the atmosphere.
defined as the (theoretical) wind that would blow on a rotating planet which results from a balance between the pressure gradient causing the initial displacement of the air, and the apparent (to us on the earth) deflecting force due to the planetary rotation. Many corrections are needed to find the 'true' wind vector amongst which are the effects of friction and the several forces involved when the pressure pattern changes - which is the usual case. However, by this definition we get the general statement that the speed of the geostrophic wind is proportional to the pressure gradient, or inversely proportional to the distance between isobars/contours. Curvature of the flow must also be taken into account ... see Gradient wind.