Urine excretion refers to the process by which waste products are removed from the blood and released into the urinary system to be eventually excreted from the body through urination. It is an essential function of the kidneys, which filter blood and remove excess water, salts, and other substances that the body does not need. The remaining waste products are then combined with water to form urine, which is expelled from the body through the urethra. In summary, urine excretion is the process of removing waste products from the body through urination.