apple-touch-iconwondering what it is ?
Well, it's similar to a favicon, except it's for the iPhone and iPod Touch menu screens. Apple calls them Web Clips.
Here's an actual example from Twitter.
<link href="http://assets1.twitter.com/images/twitter_57.png" rel="apple-touch-icon" />
You can use these elements to define the icon iPhone and iTouch users should use when they save your web appicaitons address on their device. Just like when browser users bookmark a page.
It's basically just a 57x57 pixel PNG image with no special effects applied. The device itself will add rounded corners, a drop-shadow, and a glassy reflection.
Here's some more details from Apple.