As the name suggests, DNS Prefetching is the process of resolving domain names, in advance.
Suppose a user is reading a web page, he(or she) may or may not visit a link, referenced on that web page but if he(or she) does, the next page can be loaded a lot faster if it uses DNS prefetching - because it won’t have any delay due to DNS lookup (which may takes up few milliseconds to a second or more, depending on lots of factors such as latency and whether the result is locally cached or not).
How to implement it ?
To add DNS prefetching to your website, just add an extra link tag (in head, of course), in the following format :
<link rel="dns-prefetch" href="http://example.com">
You can also control DNS prefetching at page level, using the meta tag (off means no prefetching, change it to on to enable it) :
<meta http-equiv="x-dns-prefetch-control" content="off">
Does any browser support it ?
Mozilla Firefox and Chromium/Google Chrome certainly supports this feature (with compatible syntax, the above style works well for both browsers), I’m not sure about other browsers. (I think Safari and Opera do, but you need to make sure)