On these systems, that is the recently instilled feature that allows you to determine who is allowed to use the &su& command.
(check out the WHM news section inside your web host manager)
..... you probably should get a book on linux systems administration (www.amazon.com)....
That will give you some groundwork so that you'll be able to answer many of these questions which are almost 100% related to the use of the linux operating system instead of the actual Cpanel product.
If you want some recommendations on what's actually worth reading (printed wise)... feel free to IM me.
peace.