The pressure gradient is the rate of change of pressure with horizontal distance. The steeper the gradient (isobars closer together on a synoptic chart), the stronger the resulting wind.
Driving force of wind
The pressure gradient force (PGF) is what sets air in motion, pushing it from high to low pressure. Combined with the Coriolis effect and friction, it determines wind speed and direction at the surface. On charts, areas with tightly packed isobars (steep gradient) correspond to regions of strong winds.