Here is one definition from an article found in PC Magazine Online:

"Rundll32.exe is used extensively by Windows to launch a wide variety of actions defined in DLLs. One of its many capabilities is invoking Control Panel applets. A file with the .cpl extension contains one or more applets, and some of the applets may display multiple pages. Using Rundll32.exe, you can launch any of the applets found in a CPL file, and in many cases you can cause the applet to open on a particular page."

Other information can be found here


Hope this helps clarify things.