What is removed during an illiostomy?

Possibly nothing. Ileostomy is a surgical procedure where the ileum of the small intestine is attached to a hole made in the abdominal wall. Things removed depends on the need for surgery. It can be done with a colectomy, where colon is removed as in treating ulcerative colitis. After a time the ileum may be reconnected to rectum in a procedure called a takedown or reanastamosis.
Part of intestine. Sometimes when a part of the colon needs to be removed, the ileum segment of the small intestine is connected to the abdominal wall and the excrement is collected in a replaceable bag that covers the opening and attaches to the skin of the abdominal wall.
Answer Varies. An ileostomy is created by bringing the end of the small bowel, the ileum through the abdominal wall & out to the skin. Your waste now exits into a "bag'. It can be used to divert your waste away from a problem that needs to heal, or as a result of the removal of all of your colon and rectum (including sphincters) for something like crohn's or ulcerative colitis. A colorectal surgeon can help.