Sodium chloride is the chemical name for ordinary table salt. The white crystals you sprinkle on french fries or use to season food are made of two elements bonded together: sodium (a soft, silvery metal) and chlorine (a greenish, poisonous gas). When these two dangerous elements combine, they form something completely different: a safe, essential substance your body needs to survive.

Salt has been valuable throughout human history. Cities grew up along salt trade routes, and wars were fought over access to salt mines.

Your body needs sodium chloride to help muscles work, transmit nerve signals, and maintain proper fluid balance. But it only needs small amounts. When you sweat heavily during sports or on a hot day, you lose salt along with water, which is why athletes sometimes drink sports drinks that contain sodium.

Scientists use the term sodium chloride to be precise, since “salt” can technically refer to many different chemical compounds. But in everyday conversation, when someone asks you to pass the salt, they mean sodium chloride.