Define
ISP is an acronym for Internet Service Provider. ISP's provide the connections to and from the Internet for customers to access the Internet for a price.

Detail
ISP's are often competative, usually trying to attract the most customers through upgrades in connection speeds, bandwidth and other services. Sometimes these ISP's will combine Internet phone and cable/satellite television packages along with high speed Internet. Large companies such as AOL Time Warner, Verizon Online, and AT&T SBC make up the large majority of the ISP's available within the United States.

Resources
http://www.geschaeftsbericht.telekom.de/en/co/glossar/index.php
http://www.att-signup.com/images/att150.jpg