POP = 2 meanings - Point of Presence and Post Office Protocol.

(1) Short for Post Office Protocol, a protocol used to retrieve e-mail from a mail server. Most e-mail applications (sometimes called an e-mail client) use the POP protocol, although some can use the newer IMAP (Internet Message Access Protocol). To obtain mail from POP server you should tell your e-mail software the name of your POP server and your login and password.

The POP server might be a computer with a permanent Internet connection whereas its clients might only connect to it occasionally, e.g. by modem.

There are two versions of POP. The first, called POP2, became a standard in the mid-80's and requires SMTP to send messages. The newer version, POP3, can be used with or without SMTP.

(2) Short for point of presence, an access point to the Internet. For example, if an ISP says they will soon have a POP in Cologne, it means that they will soon have a local phone number in Cologne and/or a place where leased lines can connect to their network.

ISPs have typically multiple POPs. A point of presence is a physical location, either part of the facilities of a telecommunications provider that the ISP rents or a separate location from the telecommunications provider, that houses servers, routers, ATM switches and digital/analog call aggregators.