What does it mean to bleed "out" from colon cancer?

Anemia can be first: Often a colon tumor will only be detected after routine bloodwork uncovers anemia (low blood count). Workup then should include endoscopy, and the tumor is found. Sometimes weakness from anemia prompts the same workup. It is usually a very slow, gradual blood loss, and not a sudden, high volume massive bleed.

Hemorrhage: "bleed out" is jargon for significant blood loss. Generally requires intervention like transfusion, surgery, or embolization.