A recent snapshot build of Opera for desktop has added a new feature which performs DNS lookup for the links when users hover the mouse on them. This DNS prefetching speeds up the browsing experience as it enables the browser to lookup for the targeted server in advance even before the user clicks on the link.
Google Chrome has a similar feature, Pre-rendering, where the browser loads a certain webpage in background. Opera team has not implemented pre-rendering, as no resource will be loaded in advance. Only the DNS lookup takes place, which will ultimately reduce the time to connect to the destination server and load the pages faster. This experimental feature is live only in the snapshot builds available here, and may land in the regular stable builds soon.
What is DNS look-up?
When a user directs browsers to open a web page (by clicking on any link or typing the URL in the address bar), browsers attempt to find out the IP address of that domain name. For this, the browser connects to a DNS server (name server) first. This process, known as DNS lookup, takes time and may affect the browsing experience by delaying the page loading. For more information on DNS lookup, refer this article.