What are polyps, and why are they removed?

Benign growths. Polyps are benign growths, however they can sometimes mutate into cancer, and for that reason they are removed.
Growths, prevent CA. Growths on lining of organs, stomach, uterus, commonly colon. Most are not cancers, but most cancers in colon come from polyps that grow over time, and develop into cancers. Best way to check is with colonoscopy to detect and remove polyps, before they can turn into cancer. Other tests e.g. "virtual colonoscopy" available as well, but don't allow for removal. Abnormality seen, need colonoscopy.
To check for tumors. Polyps are tissue growths that stick up from the surface of the mucosa. There are different types of polyps. Some are benign and some may serve as precursors to tumors. Colorectal polyps are detected in colonoscopy. Adenomatous polyps are cancer precursors and their removal prevents the progression of those polyps to cancer.