Answer
Pressure is defined as the force exerted per unit area by any object on another object.
Work Step by Step
Pressure is caused by the particles of gas engaging in almost elastic collisions with the walls of the container. As the gas molecules/atoms strike the walls of the container randomly, they undergo a change in momentum per unit time, per unit area. This results in force being exerted per unit area on the walls of the container, resulting in pressure.
