XML  (Extensible Markup Language)
A W3C initiative that improves the functionality of the Web by letting you identify your information in a more accurate, flexible, and adaptable way than regular HTML.

XHTML  (Extensible HyperText Markup Language)
The next generation of HTML: a hybrid between HTML and XML. XML was designed to describe data. HTML was designed to display data. XHTML is much stricter than HTML. Not all browers support XML so XHTML provides an intermediary soluton and can be interpreted by XML and HTML browsers.

ZIP
To save download time, files may be compressed, or zipped, to reduce the file size. You can unzip any zipped files with a program such as WinZip