Urine is a liquid waste product produced by the kidneys as they filter blood. It consists mainly of water, urea, creatinine, and various ions. The kidneys help maintain the body's fluid balance and remove excess substances, which are then excreted as urine. The color and concentration of urine can vary based on hydration levels and diet. Normal urine is typically pale yellow, but it can become darker if a person is dehydrated. Urine tests are often used in medical settings to assess health and diagnose conditions, making it an important aspect of human biology and medicine.