Sometimes you want to be connected to an IRC server all the time, even when you're not.
In that case you need an IRC proxy, or bouncer, that will stay connected to the IRC server(s) all the time.
That's what jBouncer does.
JBouncer is a Java implementation of a simple IRC proxy (sometimes known as an IRC bouncer). It can run on Windows, Unix, Linux, etc.
An IRC proxy is a program that connects to any number of IRC servers. You can then use an IRC client to connect to the proxy and use those servers. When you disconnect your client, the proxy stays connected to the IRC server.