Users can optionally register, which offers some benefits, but its not mandatory for most actions.
An unregistered user is sometimes referred to as an anonymous user (and the name beside their contributions will be shown as “anon”), though of course they are only anonymous in the sense of visbility to other users; to maintain integrity of The Brownbook and to provide a deterant to abuse every contribution is attributed in our database to a user’s email address. This means we can trace the author of any contribution if necessary.
A note on anonymous reviews: When reading reviews, it might be logical to assume lesser credibility to a review placed by an anonymous user, since they have elected NOT to be publicly identified. In the experience of life we generally place more credibility on opinions where the author is known.