A polyp is an extra piece of tissue that grows inside your body. Colonic polyps grow in the large intestine, or colon. Most polyps are not dangerous. However, some polyps may turn into cancer or already be cancer. To be safe, doctors remove polyps and test them. Most colon polyps do not cause symptoms. If you have symptoms, they may include blood on your underwear or on toilet paper after a bowel movement, blood in your stool, or constipation or diarrhea lasting more than a week.
Sources
MedlinePlus - Colonic Polyps