Horizontal pressure force

From Glossary of Meteorology

horizontal pressure force

(Often called, simply, pressure force.) The horizontal pressure gradient per unit mass, -α∇Hp, where α is the specific volume, p the pressure, and ∇H the horizontal component of the del operator.

This force acts normal to the horizontal isobars toward lower pressure. It is one of the three important forces appearing in the horizontal equations of motion, the others being the Coriolis force and friction.
See pressure force.