In telecommunication, the term dial-up has the following meanings:

• Dial-up access, typically to the Internet
• A service feature in which a user initiates service on a previously arranged trunk or transfers, without human intervention, from an active trunk to a standby trunk.
• A service feature that allows a computer terminal to use telephone systems to initiate and effect communications with other computers.

Source: from Federal Standard 1037C and from MIL-STD-188