draft is a possible class or package option to change the behavior of the class/package.
The draft option is often used to make the typesetting result of a class or a package easier to debug. Most classes will add a black box at the end of overfull lines with draft. Some packages try to speed up the compilation by skipping external files.
The draft option usually has a final counterpart which can be set to a single package if the class is called with draft.
You can find an (incomplete) list of classes/packages with a draft option in What does the draft mode change?.
Tag all questions with draft that refer to the usage of draft or the changes made by draft.
