Web sites have unique IP addresses that can be difficult to remember, and that is the reason that domain name systems or DNS were created. When you try to access a site through its DNS the browser connects to the server where a website is hosted and then loads the page, all of which takes not more than the fraction of a second.
DNS filtering subjects the website asked for to certain controls. This filter has blacklists that list malicious websites, or those that otherwise violate policies. It will then display a block page explaining why the site cannot be accessed until you give it specific permission to do so.
These filter controls are put in place by the ISP or service provider and can even be of help to block certain categories of sites that advocate pornography, gambling, or gaming. DNS filters have low latency and do not create any delay in accessing safe websites.