Tomcat's Catalina base and Catalina home

Sometimes you see references to tomcat/catalina home and tomcat/catalina base.  What's the difference.  The answer comes from Alessandro A. Garbagnati who writes:

"The first properties (catalina.home) points to the location of the common information, while the other property (catalina.base) points to the directory where all the instance specific information are held."

Basically, this way you can keep one copy of the Tomcat binaries yet use a different configuration by changing the directory to which base points (this directory must contain conf, logs, webapps, work, and temp).