Suction is a force created when there's a difference in air pressure. When you use a straw to drink a milkshake, suction forces the delicious ice cream to move up into your mouth.
Suction comes from the same Latin root as suck. Suction happens when a vacuum cleaner sucks up dirt or when someone sucks on a straw. At the dentist, suction is used to get rid of all the extra saliva while they work on your teeth. (Yuck.) Suction can also make things stick to hard surfaces. Some frogs can stick to windows with their little suction cup toes.