I came across a good video describing how EntocortEC works. Entocort is a corticosteroid formulated to localize its effect on the ileum and ascending colon through a delayed release mechanism. Most Crohn's disease patients have the majority of inflammation in that area, hence it is meant to be a targeted drug. Because of the targeted delivery mechanism, it is mostly metabolized before it has a chance to reach the rest of the body, limiting the side-effects that many other cortiosteroid drugs (like prednisone, etc.) can cause.
The specific drug used in Entocort is budesonide. I was quite surprised to find that it is also used to treat rhinitis (nasal inflammation).