In mechanics, the force exerted upwards by the surface that a body sits on is equal and opposite to the force exerted downwards by that body and is referred to as the Ground Reaction Force (GRF) or simply Reaction.

Your feet exert a force on the ground so in return the ground exerts a force on your feet.

The answer is reaction. A simple example is you standing on the ground. You are not moving or accelerating (in our reference frame). You are pushing down against the ground with a force (the action) equal to your weight. The ground pushes back up (opposite direction) with an equal force (the reaction force).

While pushing we actually apply force on the ground which is opposed by frictional force acting on our feet.The ground now applies a normal reaction force on us which we apply on the body to be pushed.

Any object moving or stationary that is on the ground is subjected to a normal/reaction force upwards.