What's an MBean or JavaBean?

A fancy name for a Java class that:

1. is serializable
1. means you can write/read the contents directly to disk as is
2. has a 0-argument constructor
3. has getter and setter methods
1. Have you ever tweaked a mbean value via jconsole before, btw?

Understand, there was major hype for Java back in circa 2000 that didn't quite pan out as expected.