Suction is when something is pulled into a space because the pressure there is lower than the pressure outside.
Suction is often used to clean things or to move things without touching them.
Examples:
The suction from the vacuum cleaner picked up the dirt.
When you drink from a straw, you use suction to pull the liquid into your mouth.
The suction cup stuck to the window.
The suction from the plunger was very strong!
The suction from the spaceship was so strong, it pulled everything in.
The suction from the drain was so strong, it pulled in all the water.