The force that resists the motion of an object through a gas and liquid is called drag.
For objects moving through air sometimes instead of drag the term air resistance is used. As an object moves through air, the gas molecules in the air push against the surface of the moving object resulting in friction between the gas molecules in the air and the surface of the moving object.
The amount of drag encountered depends on the following:
An object with smooth lines will allow the air to flow over it more easily reducing the drag. This is known as streamlining and is why objects built for speed such as racing cars have smooth bodies.
Drag increases with speed.
The larger the area of contact the more drag it will experience.
The type of fluid
There will be more drag in a liquid compared to a gas as the molecules are a lot closer together. A stone will fall much faster in air than in water.