COMMON EXTENSIONS .edu Educational organization (most US universities) .k12 US school site (not all US schools use this) .ac Academic institution (outside of US) .sch School site (some schools outside of the US use this) .com Company (usually .co in the UK) .org Any organization .gov Government agency .net Network New extensions to look for are .biz, .name, .pro, .info. All are used for commercial purposes. Extensions can also include country codes, such as .uk, .ca, .za, etc. .mil Military institution
The tilde ~
The tilde ~ followed by someone's name, tells us that this is a personal posting and not an official website for the domain. Example: http://pubweb.northwestern.edu/~abutz/di/intro.html
Google ranks results based on popularity. It counts the number of links from sites all around the Web. For example, if a large number of sites has a specific keyword somewhere on their Web site along with a link to a particular site, Google counts the number of times the keyword appears along with the number of links to a particular site. The higher number of links to a site, the higher Google will rank that site on a list of results.