What does blood in stool signify?

Many causes. Blood in the stool can be caused by a variety of problems. You need to be seen by a health care professional.
Abnormal. Remember and I have said it many times, any blood in the stool is abnormal and needs to be evaluated promptly by a specialist, either GI or colorectal. Do not delay. Most of the time it is benign hemorrhoidal bleeding but in the few cases where it is due to something more serious, early detection can save lives.