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POP Definition & Meaning

POP/PoP can be used to refer to one of the following concepts:

Post Office Protocol

Post Office Protocol (POP) is a protocol used to retrieve email from a mail server. POP has seen a few versions since its initial release in 1984. POP2 was released in 1985 and POP3 in 1988, but POP3 has become the primary version in use today because of its security and performance features.

Many email clients offer both POP and Internet Message Access Protocol (IMAP) to access email messages. Compared to IMAP, POP is more straightforward and secure, but it may also be less efficient because it manages messages locally as opposed to storing them on a central server. Some email applications prefer IMAP over POP because this distinction allows messages to be synchronized across multiple devices—an important feature for mobilization. Neither IMAP nor POP should be confused with Standard Message Transfer Protocol (STMP), which is used for sending messages to a mail server so that IMAP or POP can be used to retrieve them.

Point of Presence

A Point of Presence (PoP) is a demarcation point or physical location that provides access between two or more networks or devices. PoPs are often used as an access point to the Internet, and Internet Service Providers (ISPs) typically have multiple PoPs. These include facilities (sometimes shared with a major telecommunications provider) that house servers, ATM switches, and digital/analog call aggregators. A PoP can be detected when equipment with connectivity functions are present, including routers, firewalls, and client devices.

Programmed Operator

A Programmed Operator (POP) is a pseudo-opcode in a virtual machine language that is executed by an interpretive program. This concept of POPs was developed for the SDS 900 series in the 1960s and was based on the concept of "extracodes" found in the Atlas computer systems. The POP instructions provide the ability to define an instruction set for efficient encoding by calling subprograms into primary memory.


Picture-outside-Picture (PoP) refers to the way of viewing multiple pictures (windows, applications, etc.) simultaneously in which both pictures are positioned side by side. This is in contrast with Picture-in-Picture (PiP) displays that allow two or more pictures to be layered on top of one another. With PoP displays, the pictures are given equal size and dimensions, so they are particularly common amongst security monitoring systems or other environments where multiple views need to be monitored with equal attention.

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