Urinary tract infection: An infection of the kidney, ureter, bladder, or urethra. Abbreviated UTI. Not everyone with a UTI has symptoms, but common symptoms include a frequent urge to urinate and pain or burning when urinating. More females than males have UTIs. Underlying conditions that physically obstruct and impair the normal urinary flow, such as the formation of cysts within the urinary tract, can lead to complicated UTIs. Treatment usually involves increased fluid intake and use of antibiotics. In cases where physical obstruction is present, special medications or surgery may be necessary.