Wikipedia:Wikipedia is anonymous

As an editor on Wikipedia, you will have a choice: You can let everyone know who you are by using your real name. Or you can make your edits with a pseudonym, hiding your true identity, and keeping it to yourself.

Remaining anonymous is your right. But there are ways in which your identity can be revealed, even if you do not wish. In other words, on the Internet, nobody knows you're a dog,  tell them you are.

For example, if you are so proud of an article you created that you tell people you know in person, they may read the article, and from looking at your contributions, they can then learn what else you did on Wikipedia. It is very possible that you do not wish for these people (who could be your relatives, friends, or even your boss) to know about other edits you have previously made or that you plan to make in the future. So before you go and brag, you may wish to be aware of this.

You may also get to "know" other editors on Wikipedia (without knowing their true identities) if you work on a project or on many articles within a common area. These are people you may end up in deep discussions with. You may not want them to know about your other areas of interest.

Hiding such edits from your edit history is a legitimate use for having a second account.

Voluntarily sharing your identity
There are various ways in which you can share your identity with others if you do wish:
 * Your username: You can make your username your own name, or a name that will be directly tied into your own identity (at least to those who know you). Or you can use a pseudonym, making it one through which no one can determine who you are.
 * Your user page: You can provide information regarding your identity on your user page. Or you may leave this out. You do not even need a user page if you do not wish to have one.
 * Discussions: Sometimes, there will be moments within discussions where it will be acceptable to reveal your identity. You are never under any obligation to do so, but this can occur.

Details of your identity
There are various details of one's identity that may be kept secret, but may be revealed by one's editing patterns.
 * Gender/Race/Religion/Ethnicity: There is no need to reveal one's gender, race, religion, or ethnicity. But by looking at one's edit history, the articles one has edited may be those of interest to members of a particular group.
 * Geographic location: There is no need to reveal where you live. But it is pretty common for people to make at least some edits to articles pertaining to the area where they live, and to have familiarity with these subjects. In order to avoid revealing where you live, if you wish to edit articles pertaining to your locality, create a separate account for this purpose or edit a variety of locality articles.
 * Interests: If you edit articles pertaining to a particular interest, particularly a place where you live or an unusual hobby, someone who knows you may be able to detect your writing style and specialized interests and determine you made these edits.

IP editing
Many people refer to IP editing as "anonymous editing." But in reality, IP editing is less anonymous than registering a username. IP addresses in many cases can be traced to an exact location. On the other hand, if you create an account and edit under that, your IP address will be hidden from most users (though it can be obtained by a certain few users only if warranted).

A tool called WikiScanner enabled the IP address used for any IP edit to be traced to an approximate location, though it is no longer online. In some cases, it was used to determine that edits to an article about a company have been made from the company itself, which is often a conflict of interest.

This news story describes how WikiScanner was used to reveal that thousands of Wikipedia edits were allegedly made from the offices of various government agencies on taxpayer-funded time.