Infection of any of the organs of the urinary tracts such as those of kidneys, Ureters (tube between kidney to bladder), urinary bladder, and urethra, may broadly be called as UTI. Specifically following terms are used: pyelonephritis or nephritis (infection - inflammation) of kidney; ureteritis (for ureters), cystitis (urinary bladder), urethritis (urethra). Pyelonephritis is generally the serious condition.