Zen coding is smart and fast way of writing the html, xml and xsl code. Its a plugin that has a powerful abbreviation engine that allows to expand expressions into HTML codes.
The video shows how to use the powerful technique to save time. Offcially supported editors include Aptana/Zend Studio/Eclipse, Textmate, Coda, Notepad ++ and many more.
A full list of fetarues and supported editors and third-party supported editors can be found here.