Hematuria is defined as the presence of red blood cells in the urine. It can be characterized as either "gross" (visible to the naked eye) or "microscopic" (visible only under the microscope). Microscopic hematuria is an incidental finding often discovered on urine tests as part of a routine medical evaluation, whereas gross hematuria could prompt you to visit the doctor. Hematuria can originate from any site along the urinary tract, including the kidneys, ureters, bladder, prostate and urethra.
Links

http://kidney.niddk.nih.gov/kudiseases/pubs/hematuria/
http://www.mayoclinic.com/health/blood-in-urine/DS01013
https://www.urologyhealth.org/educational-materials/hematuria