ISP = Internet Service Provider (also known as: Internet Access Provider). The major Internet Service Providers are: America Online, AT&T Worldnet, CompuServe, Cox@Home, Earthlink, PacBell DSL, Road Runner (Time Warner), and SBC Yahoo Globalnet.
There are hundreds of other smaller local Internet Service Providers.
As its name suggests, an Internet Service Provider provides access to the Internet. This access can be: 1) through the phone lines with a regular dial-up modem (which is like a little telephone inside your computer), or through a DSL modem, which is much faster than through a dial-up modem, but uses the same phone lines; 2) through your cable TV cable, which is how the Road Runner and Cox@Home services work, or 3) through satellite service, such as the Starband or DirectPC services.