Saline 0.9%, also known as normal saline, is a sterile solution of sodium chloride (salt) in water. It contains 0.9 grams of salt per 100 milliliters of water, making it isotonic with human blood. Saline 0.9% is widely used in medical settings for hydration, intravenous (IV) therapy, wound cleansing, nasal irrigation, and as a diluent for medications. It is safe, well-tolerated, and essential in various healthcare applications.