A Shoutbox (AKA: Saybox, Tagboard, or Chatterbox) is a chat-like feature of some websites that allows people to quickly leave messages on the website, generally without any form of user registration.
In their simplest form, shoutboxes are simply lists of short messages, possibly with information about their authors. The page may be automatically refreshed after a certain interval, or polled dynamically in order to keep new messages visible. Older posts are often deleted after a certain number of messages have been written in order to preserve space on the server.
Shoutboxes are usually maintained in a manner similar to that of more complex boards, with moderators that can delete posts and ban usernames or IP addresses. Occasionally, features such as impostor identification, flood control, and profanity filters may be included.
Like most dynamic content, shoutboxes typically interface with a database, and some may query the database every time a page is requested. Additionally, a shoutbox may be loaded from a simple file. Unlike most dynamic content, however, shoutboxes are generally placed on every page of a web site, so they tend to cause disproportionate strain on databases. Therefore, care must be taken to ensure that shoutboxes do not use too many database resources. (Caching systems like memcached can be used to mitigate this to some extent, or an alternative implementation such as storing all messages in system-wide shared memory rather than a database may be used)