Internet Service Provider. Your choice of an ISP can either be bery wise and beneficial, such as choosing SBCYahoo! or EarthLink, or give you an idea of what Hell is like, by choosing AOL.
Words cannot describe how much AOL sucks. Worst ISP ever.
The local networks most normal people have to dial itno to reach the Internet; ISPs, in turn, makedeals with such Internet backbone owners as MCI in order to connect to the Internet.