ISP

The company that you pay money to get Internet. If you pay nothing, then perhaps you pay a municipal tax for this, or some people just like you or something.

An ISP handles administration of getting you online, they pay for the Radius servers to authenticate you, they manage mail servers to get you email, they may even give you a small webpage and those servers they pay for. They retain your login history by law for a number of months (at least in europe) and hand it to law enforcement with a court order, in case you're being investigated.

It's important for ISP's not to have lock-in contracts for their customers and your access should be set so that you can replace your ISP rapidly. This creates competition for the best ISP and gives the user buying power for the best product. Lock-in contracts of 12 or 24 months is silly.