What word does your mother always say?
(IAP) A company or other origanisation which provides access to the Internet to businesses and/or consumers. An IAP purchases an Internet link from another company that has a direct link to the Internet and resells portions of that bandwidth to the general public.
For example, an IAP may purchase a T1 link (1.544Mb/s) and resell that bandwidth in chunks consisting of ISDN (64Kb/s, 128Kb/s) and analog modems (14.4Kb/s, 28.8Kb/s). The IAP's customer base is likely to include both businesses and individuals. Individual customers usually connect to the IAP via a modem and telephone line to a (preferably local) point of presence.
An IAP may also be an Internet Service Provider.