The substance that decreases friction is called a lubricant.

Here's a breakdown:

* Friction: A force that opposes motion between two surfaces in contact.

* Lubricant: A substance that reduces friction between surfaces. It does this by creating a thin layer between the surfaces, separating them and allowing them to move more easily.

Examples of lubricants include:

* Oils: Motor oil, cooking oil

* Greases: Grease for car bearings

* Water: Used as a lubricant in some industrial applications

* Air: Can act as a lubricant in some situations

Let me know if you have more questions about friction or lubricants!