Almost every episode of Shameless and Shameless (US) includes a short, usually humorous scene after the ending credits. This is the Post Credit Scene and every episode page should include a description of what happens in that episodes post credit scene.
Please note that the post credit scenes of Shameless (US) occur not after the credits have ended, but in the middle of them. Usually a page or two of credits will be shown before the scene, with the credits continuing after.
Due to the humorous quality of post credit scenes it is likely that they aren't always meant to be more than a joke, as some provide some nonsensical yet funny information, for example that Lillian Tyler has a penis.
In the commentary of many episodes of Shameless, various crew members refer to the Post Credit Scene as the Credit Breaker.