A favicon (short for favorites icon), also known as a shortcut icon, website icon, URL icon, or bookmark icon is a 16×16 or 32×32 pixel square icon associated with a particular website or webpage. The interesting bit here is the apple-touch-icon which is used if you save a bookmark to your home screen on an apple touch device such as an iPad or iPhone. Interestingly enough, android also supports its usage. The apple-touch-icon default size is 57px by 57px. As the comment says, if your icons are in the root of your domain, these links aren’t required.

<!-- Place favicon.ico and apple-touch-icon.png in the root of your domain and delete these references -->
<link rel="shortcut icon" href="/favicon.ico">
<link rel="apple-touch-icon" href="/touch-icon-iphone.png">
<link rel="apple-touch-icon" sizes="72x72" href="touch-icon-ipad.png" />
<link rel="apple-touch-icon" sizes="114x114" href="touch-icon-iphone4.png" />
<link rel="apple-touch-icon-precomposed" href="/touch-icon-android.png"/>