Table of contents
TOC is a common three-letter acronym (TLA) for 'Table Of Contents'. On MediaWiki sites, a table of contents is included automatically on the left margin of a page just before the first headline if there are four or more 'Headlines' (primary sub-headings) in an article.
You can force a TOC in an alternate position on the left margin by placing
__TOC__ at the point where you desire said TOC.
You can prevent a TOC from appearing anywhere by placing
__NOTOC__ anywhere within the edit box, though there ought to be strong reasons or justification for hiding a table of contents.