The administration of a clear liquid diet with laxatives, enemas, or both, in anticipation of endoscopy of the lower gastrointestinal tract to provide an optimal view of the bowel wall. (Source)
a cleansing of the intestines from fecal matter and secretions...The ultimate goal of bowel preparation is to empty and cleanse the bowel for a diagnostic procedure (using x-rays to detect a disease process in the intestines) or for surgical intervention (such as removal of polyps) (Source)