Urine is liquid biological waste excreted by the kidneys. The human body produces urine, as do all mammals, reptiles, birds, fish, and amphibians. Urine is mostly water, and also contains urea, creatinine, waste enzymes and hormones, proteins, carbohydrates and fatty acids. Urine also contains large numbers of bacteria, so coming into contact with or ingesting it is unhygienic and can be harmful.
Sociologically, urine's smell and the potential harm it can cause in terms of infection make it taboo in many cultures. Urinating on objects is sometimes done in order to show extreme disapproval, or to humiliate, although such behavior has no place in civilized society.