An equilibrium is a state of a system where all forces acting on the system is balanced. A system that is in equilibrium does not change. The word has been used for different concepts from different fields of study.

• Hydrostatic equilibrium applies to liquids.
• Thermal equilibrium means as much heat is entering and leaving something.
• Homeostasis is a living thing keeping its internal balance.
• Equilibrioception is how an animal stands upright.