I use a lot of snippets when I program, those little shortcut that transform several lines of code. Zen coding goes further by proposing to use snippets the same way as the CSS selection.

For example the following line of code:

div#header

is tranformed into:

<div id=”header”></div>

And this:

div # header> p> lorem

is transform into :

<div id="header">
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor
incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud
exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure
dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur.
Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit
anim id est laborum.<p>
</div>

For more information see :http://code.google.com/p/zen-coding/