A Jabber ID is a unique identifier used in the Jabber/XMPP (Extensible Messaging and Presence Protocol) network for instant messaging and presence information. It typically resembles an email address, formatted as username@domain, allowing users to connect with others on the same network or across different networks. Jabber IDs enable users to send messages, share files, and see the online status of their contacts. They are commonly used in various applications and services, including Google Talk and WhatsApp, facilitating real-time communication over the internet.