Rectal bleeding: Blood passed rectally. Blood in the stool can be bright red or maroon in color. Larger amounts of blood that remain in the intestine long enough can turn the stool black. Blood in the stool also may be invisible to the naked eye (occult).
The causes of blood in the stool range from harmless, annoying conditions of the gastrointestinal tract such as hemorrhoids to very serious conditions such as cancer. Blood in the stool should be evaluated by a healthcare professional.