When Chatter is enabled on an object, users viewing a record of that object see a rich user interface to manage posts and comments, followers, and their interest in following the record. This same native user interface functionality is also available to Visualforce developers. Using Chatter components, you can embed the same Chatter toolbar, in its entirety or in pieces, within your custom user interfaces.
Chatter is supported in Visualforce through eight dedicated components in the
chatter namespace, and an additional Chatter-specific attribute on the generic
detail component, as described here: