Wiktionary
n. Any force acting normal, to a surface, or perpendicular to the tangent plane.
Wikipedia
In mechanics, the normal force $F_n\$ is the component, perpendicular to the surface (surface being a plane) of contact, of the contact force exerted on an object by, for example, the surface of a floor or wall, preventing the object from falling. Here "normal" refers to the geometry terminology for being perpendicular, as opposed the common language use of "normal" meaning common or expected. For example, consider a person standing still on the ground, in which case the ground reaction force reduces to the normal force. In another common situation, if an object hits a surface with some speed, and the surface can withstand it, the normal force provides for a rapid deceleration, which will depend on the flexibility of the surface.
Usage examples of "normal force".
He maintained that among other faculties of the Antis they had the ability to structurally strengthen and stabilize a normal force field by means of some sort of physical catalytic emanations.
Ambrosius had, in fact, modelled his own army on the force of the Saxon Shore, a marvellously mobile fighting instrument which could live off the country and do everything at twice the speed of the normal force.