Postrenal obstruction refers to a blockage that occurs in the urinary tract after the kidneys, impeding the flow of urine and potentially leading to kidney damage. It is clinically significant as it can result in hydronephrosis, renal impairment, and acute kidney injury if not promptly addressed. A common cause of postrenal obstruction is benign prostatic hyperplasia in older males, which can lead to urinary retention and subsequent complications if untreated.