An IRC Bouncer (BNC for short) is a software package that is used in a similar way to a proxy. A BNC allows the user to hide there real IP address when connecting to an IRC network which gives the user a sense of security and privacy. A user connecting to an IRC network through a BNC will usually connect with the host "ident@BNC.Provider.net" where as normally they would connect as "ident@MY.IP.Address".
BNCs have many other features such as the ability to stay connected to IRC networks 24/7, even when all clients. Whilst away, one can log private messages, and have automated scripts which alerts others that one is away. Many BNCs support loading scripts and modules to enhance the users experience.
Although BNCs usually run the same and have the same features, there are a few different groups that have made their own variation on the BNC software.