A stub is an article containing only a few sentences of text which is too short to provide coverage of a subject, but not so short as to provide no useful information. Sizable articles are usually not considered stubs, even if they lack wikification or copy editing. With these articles, a formatting template is usually added instead of a stub template. Note that if a small article has little properly sourced information, or if its subject has no inherent notability, it may be deleted or be merged into another relevant article.
How to change a stub to a full article
To change a stub to a full article the article needs expanding, to include all the relevant information on the subject. It is important that when a stub is expanded that the policies of the site are followed, otherwise it is likely that the article will get marked for formatting issues.
A list of the current stubs can be seen here.