Equilibrium is a state of balance. If you play sports so much that you don't have time for your studies, you need to study more and play less, until sports and studying reach a point of equilibrium. Or become a professional athlete.
The word equilibrium is commonly used to refer to mental or emotional balance, and a near synonym in this sense is composure. In chemistry, equilibrium is the condition existing when a chemical reaction and its reverse reaction occur at equal rates. This noun is from Latin aequilībrium, from the prefix aequi- "equal" plus lībra "a balance, scale."