Prefetch allow the browser to fetch a defined document, it could either be a picture, or a web page. The fetching happen while the browser is idle.
<link rel='prefetch' href='/assets/img/image.png'> /* content */ <a href='/pageB.html'>
The user click on pageB link after reading the content (let some time for the browser to cache the pictur on pageB)
Page B is loaded very fast because the picture is already cached by the browser.
Using google analytics, prefetch could be used to cache the page which receive the most rebounds from the landing page. According to rocketmill this features is only supported on chrome and firefox but with differents keywords
For cross browser compatibility, it would be preferable to use
<link rel='prerender prefetch' href='/assets/img/image.png'>