That is an IP address in the LoopBack range. IP 127.0.0.1 is known as the TCP/IP v4 Diagnostic Responder.
When one wants to block access to a web site, one can force resolution of a Domain Name to a LoopBack address. This redirects packets from going out to the Internet and point right back at one's own PC.
Such filtering can be done on a DNS Server, through an installed application or the etc/hosts file.