Internet Service Provider. This is the company that supplies your Internet connection. It could be your phone company or your cable company. (Almost) all ISP’s offer email with your connection. So, if your ISP is the phone company CenturyTel, then you may have the email address SoAndSo@centurytel.net. This means you are using the free email address offered by CenturyTel with your paid Internet service. Sort of like the phone company used to give you a free listing in the phone book because you paid for phone service.
NOTE: You aren’t required to use your ISP’s email. You can sign up for a free Hotmail, Yahoo or Gmail account and bypass your ISP.
Even better note: If you DID sign up for a free Hotmail, Yahoo or Gmail account and you sign up with a different ISP, you don’t have to change your email address. Presto! Freedom.