What is WHM?
CPanel / WebHostManager (WHM) is an all in one system that allows simple administration over your web server, while offering the client a powerful web based interface to control all kinds of functions that the CPanel interface has to offer. The system also keeps itself up to date with the latest package upgrades and is always being enhanced to make it a more and more powerful system.

What is cPanel?
CPanel is a web based client interface. It allows users to monitor things like disk space and bandwidth usage. CPanel also gives the client the ability to manage his own passwords, Mail accounts, FTP accounts, sub domains, error pages, protected directories and files, MySQL Databases, Cron jobs, redirects and much more. The client interface also gives Boards and the list of pre-installed scripts.