Users who are not logged in are called unregistered users, or IP users. These users can edit pages which are not protected or semi-protected; their edits will appear in page histories alongside the IP address from which they were made.
On Wikimedia wikis, unregistered users were originally only at a minor disadvantage to registered users, but as time passed, more features have become unavailable to them. Unregistered users cannot move pages, upload media, or maintain a watchlist. On the English and Persian Wikipedias, they cannot create pages outside of the "talk" namespace. Because IP addresses are sometimes dynamic, an IP-based user page can be impractical, and in fact it is disallowed on some wikis. Unregistered users are sometimes prohibited from participation in processes such as deletion and permissions debates, or can only participate on a restricted basis (e.g. can leave comments, but cannot vote).
Unregistered users also are not able to select the option of minor edit as this could allow a bad-natured user to make undesirable changes and not be spotted for some time.
Unregistered users are also sometimes referred to as anonymous users, or anons, as opposed to pseudonymous users (usernames on Wikimedia wikis are mostly pen names, not real names). However, this is ambiguous and, strictly speaking, incorrect. The public visibility of an unregistered user's IP address means that their geographical location and/or the organization from which they are posting can be looked up. Also, in extreme legal cases, the computer from which the user contributes could be identified through a subpoena to the ISP, which can eventually lead to identification of the user. In this sense, unregistered users are in fact less anonymous than registered users who do not reveal any personal information.