For any object moving through a fluid, forces are applied to the object as the fluid moves around it. A fluid can be something like water, or even something like the air around us. When the object is specifically designed to maximize the forces that the fluid can apply, you can designate these designs as airfoils. A more common name that most people would use is a wing. The shape of a wing, or airfoil, determines the forces that are applied to it when it moves through a fluid or the air. These forces also depend on the speed of motion through the fluid and the direction of flow around the airfoil.