What is suction? What is suction? The act or process of sucking.A force that causes a fluid or solid to be drawn into an interior space or to adhere to a surface because of the difference between the external and internal pressures.To draw away or remove by the force of suction: suction fluid from the lungs. To clean or evacuate (a body cavity, for example) by the force of suction.Creating suction.Operating or operated by suction.