Deletion of a Wikipedia page removes the complete page (and all previous versions) from public view. Deletion happens when a page is unsuitable, unhelpful, or does not meet the required criteria. Two further deletion processes exist to address undesirable material that may have been added to a page or visible in a log. The deletion policy explains when deletion is acceptable.
This page explains the processes available, and how deletion discussions work.
You may have come here because a deletion notice of some kind was added to an article that you wrote. Please read this guide to see what happens now and how you can be involved in the decision.
Any user may suggest deletion of a page for good cause. However, pages may only be deleted summarily via the speedy deletion process if certain criteria are met. In cases of a borderline article, a notice of proposed deletion may be used, giving time for response. In all other cases where removal of an entire page is being considered, a "deletion discussion" happens. The main deletion process for encyclopedia articles is known as "articles for deletion" (AFD). Other kinds of pages have similar processes.
Undesirable text can be removed by anyone by editing the page. However, the text will remain publicly accessible in the article history. If this is unacceptable, then an administrator can permanently delete the content, and it will only be visible to administrators. This is called "revision deletion"; to request it, see how to request revision deletion.
A form of extreme deletion known as Oversight also exists, which is operated by a very few specially authorized users. Users with Oversight access can often remove certain serious privacy-breaching and defamatory material so that even administrators cannot see the material. This is requested by email via requests for oversight.