To perspire means to sweat. When you run around the playground on a hot day or work hard during gym class, your body releases moisture through tiny openings in your skin called pores. This moisture is perspiration, and the act of releasing it is perspiring.

Perspiration is one of your body's most important cooling systems. When you get too hot from exercise or warm weather, your brain signals your sweat glands to release water onto your skin's surface. As this moisture evaporates into the air, it carries heat away from your body, cooling you down like a natural air conditioner.

Perspire is a more formal or polite word than sweat. You might hear someone say “I was perspiring during my piano recital” instead of “I was sweating.” Both mean exactly the same thing, but perspire sounds a bit more refined.

When you see athletes perspiring heavily during a game or notice your own face perspiring after climbing stairs, that's your body doing exactly what it should to help keep you at a healthy temperature.