You have probably seen an "about:" URL at some point in your browsing life. Most people will never think twice about it, others may feel a slight pique and wonder, why? This article if for those whose curiosity gets the best of them and inevitably searches the internet for an explanation.
The most commonly seen "about:" URL is "about:blank", It is in every major browser and loads an empty page. For a list of "about:" URL's in your browser try this: "about:about"
Why is it called "about"? The short answer is that it was supposed to be "about" the people building your browser. I added the original "about:" URL as an Easter egg in version 1.0 of Netscape Navigator. I was working on the cross platform networking and page loading code and I got the itch one day to add an Easter egg. The URL format allows for any new prefix to be added, so I created the new prefix "about" so that we could have a page for the engineering team to be listed. As part of my work I created a framework so that any block of HTML could be loaded and addressed by an "about" URL.
One of the original about URL's that is still in the firefox browser is "about:mozilla", which shows a fictitious pseudo religious phrase glorifying our mascot Mozilla.
There were also URL's for most of the original engineering team. ari, atotic, blythe, chouck, dmose, dp, ebina, hagan, jeff, jg, jsw, jwz, karlton, kipp, mlm, montulli, mtoy, paquin, robm, sharoni, terry, and timm
In the early days there was also one special feature of my "about" URL "about:montulli", it would take you to a random page in your history, I'm not sure why, I just thought it would be an interesting feature.
"About:blank" which is the most commonly used URL today was created so that the new window targeting features of Netscape 2.0 could load a URL that was empty. Such a thing didn't exist prior to that and we needed a way to create a new window with no content, or to have your browser load with no URL. The about framework already existed, so we reused it to load a blank page. The rest of the "about" URLs evolved due to the same reason. We already had an "about" URL and we kept reusing it for "config", "cache", "history", etc...