1. Post Office Protocol, a protocol used to receive e-mail from a mail server. See POP3 While POP clients can be configured to leave mail on the server, typically they delete the messages, once read; the result is that the email is only available on the computer it's originally read on. The IMAP protocol is different in that it leaves the email on the server, making it possible to read email from more than one computer.
2. Point of Presence, an Internet Service Provider's physical connection to another telecommunications network. Often found in a colocation centre. Most users only need to know about POPs for telephone dial-up access. An medium to large sized ISP generally has many POP's, some have hundreds, some even thousands.
3. PowerPC Open Platform, a computer hardware reference design released by IBM for free use in 1999. The successor of CHRP.
4. Probability of precipitation, used in a weather forecast to define the chance that rain, snow, or other precipitation will fall during the specified period.