A company that sells a service that allows you to connect to the Internet via DSL, cable, modem, or satellite. Most offer you an email address, and can also offer you the ability to create a personal web page.
A company that sells Internet connections via modem (examples: BSNL, VSNL, NIC, ERNET and many other private agencies). Faster, more expensive Internet connectivity is available via cable, DSL, ISDN, or web-TV.