GPL Stands for General public license. The most widespread such license is the GNU General Public License, GNU GPL or GPL for short. This software license is available in differrent versions and used by Joomla and many other FOSS projects. Joomla is licensed under GPL2 now.
Hit Records the number of times a specific page or item is accessed. Joomla tracks hits for many item types, for instance, an article or a banner ad.
CSS A Cascading Style Sheet or CSS is used to control the presentation of an XHTML page. For example, a CSS file will often control the font, margins, color, background graphics, and other aspects of a web page's appearance. CSS allows you to separate the content of an XHTML page from it's appearance. In Joomla!, CSS files (for example, template.css) are normally part of the template. Reference: http://docs.joomla.org/Glossary
