What is the difference between the anus and the outer part of the posterior, and is the anal opening considered the inner part of the posterior, such that the fast is broken by the entry of something into it?

The outer part of the anus is the anal opening, and like the outer part of the body, it must be washed during ghusl (ritual bath) after janaba (state of ritual impurity). It is permissible for a husband to enjoy it. As for the inner part of the anus, some scholars held that the entry of anything into it invalidates the fast, while others favored non-invalidation, as it is not considered a jawf (internal cavity).