BSL Physics Glossary - friction - definition
Translation: When two surfaces rub together, friction is produced. If the two surfaces are rough, when they rub together they become hot. When two smooth surfaces rub together they do not become hot.
For example, why do you fall over when walking on ice? Because there is not much friction between your feet and the ice. But if you walk on carpet the surface is rough so the friction is high. This mean you can walk around easily without falling. So surfaces can have low friction or high friction.