What does "input type=hidden" mean?

In hypertext markup language, a hidden input field is a special kind of input field that holds values that are not intended to be seen or changed directly by the user. The contents of hidden fields are not visible on the Web pages.

Because Web servers are stateless, which means that they do not maintain information about previously served Web pages, it is often necessary for more complex websites to find ways to keep track of the actions that a user has taken earlier. One way to achieve this is to put such information inside of the hidden input fields.