Plesk is a full-featured web-based control panel that allows you to manage your domain through a web interface. The idea is to transfer as much of the control and responsibility of managing your web site to you. You have the ability to manage all aspects of email, files, FTP, and web site statistics.

Cpanel has more features over plesk while Plesk is simpler to use and has about 60% of the features found in Cpanel.

Full Plesk user documentation and feature list can be found here.