Cleanup refers to the process of improving articles which have been deemed 'messy'. An article may be deemed as such if it has poor spelling, grammar or punctuation, or if it is not laid out well according to the Wikipedia manual of style and the conventions used on this wiki.
A current list of articles marked as requiring cleanup can be found in the cleanup category.
Nominating an Article for Cleanup[]
Please add the cleanup template at the top of the article, adding a datestamp (see Template:Cleanup for usage).
{{cleanup|~~~~}}
Then, if it is not immediately obvious why you have tagged the page, put something on the talk page to indicate what needs cleaning up.
Cleaning up an Article[]
Anybody is welcome to clean up articles. Take a look at the cleanup list to find an article that needs cleanup, and reformat it as well as you are able. Once you are done, add something to the article's talk page to say that you have cleaned it up, and remove the cleanup template so that it is no longer marked.