What Are Points of Presence (POPs)?
A computer network is spread out to many different locations. The larger the network, the more connection points there are in that network. A Point of Presence (POP) is a physical location where a certain network or ISP has a piece of equipment at. These POPs are places where others can connect to that network.
For a network to sell Internet access to users, the network must have a router or switch that the users can then connect to. Residential ISPs build out cables to each house and provide each house with a cheap little router to allow the household to connect to the ISP. A backbone network provides long distance connectivity. There are many networks that do not offer "last mile" or residential services. Instead these networks offer Internet connections only within certain physical locations.
These physical locations are POPs where that network has a peice of networking equipment that allows data to be sent into and out of that network. This is usually a router, but can also be a switch. A customer would connect to that network at the POP and get connectivity to the rest of the Internet from there.
To get service at one of these POPs a customer must either be located within the same building or must purchase layer 2 transport into that location from a third party.
Networks will display a list of their POPs to potential customers. This is a list of physical locations where those customers will have to be able to connect to to receive service from that network. If the customer is unable to find a way to reach one of those POPs, then they likely will not be able to purchase an Internet connection from the network.
The POP is the physical location where a network has a piece of their core networking gear.