All j-pouches are created to replace the rectum, thus are considered a "neo-rectum."
Most members here have an ileal j-pouch, made from the small intestine and have had a complete removal of the colon and rectum for ulcerative colitis or polyposis.
In the case of rectal cancer with a low anterior resection, a colonic j-pouch may be created to replace the rectum.
The difference between the two is that a colonic j-pouch will produce a function more similar to a normal colon and rectum, while an ileal j-pouch will have normal function of more loose stool and higher frequency, because of the lack of a colon to absorb water.
They do not make a BCIR or other continent ileostomies unless you have no colon left. Those are always ileal pouches.
Hope this helps.
Jan 