A connection to the Internet via Serial Line Internet Protocol (SLIP) or Point-to-Point Protocol (PPP). For this, you need TCP/IP software on your computer. When connected by SLIP/PPP, your computer actually becomes another node on the Internet. You can then run popular client software, such as network applications, directly. This has an advantage over a shell account, where you have to "double download" in order to transfer a file by FTP (because the data goes to a network first and then to a local machine).
While SLIP and PPP are largely similar, there are some key differences. PPP is a newer protocol that's better designed and more acceptable to the sort of users who like to standardize protocol specifications.