A JID or Jabber Identity (also called a Jabber ID) is the username or account name used to access a Jabber account.
They usually take the form in a similar way to email addresses.
The resource component enables a user to contact a particular access point logged into each account, e.g. and . The resource component is not necessary in order to contact a Jabber user.
Transports, agents, and other automated parts of the Jabber network may not have a user part to the JID. A common example would be the AIM transport, where the transport itself has a JID along the lines of , and contacts on AIM would appear as .
In a similar way to Sendmail, accessing other protocols is possible with Jabber transports. Users can then contact from a client such as MSN Messenger using the JID form .
Limitations
Jabber usernames are limited to 1023 characters and the following characters are not allowed: ("at" sign) (colon) (single quote) (double quote) (open angle bracket) and > (close angle bracket) (ampersand) (carriage return), (newline), (tab) and any other control character white space