Hi
HQ is usually referred to as Central Office.
Depending on the company size and requirements, they either build their own Data Centers or use a POP location to host their equipment.
"A point of presence (PoP) is an artificial demarcation point or interface point between communicating entities. A common example is an Internet point of presence, the local access point that allows users to connect to the Internet with their Internet service provider (ISP).[1] A PoP typically houses servers, routers, network switches, multiplexers, and other network interface equipment, and is typically located in a data center. ISPs typically have multiple PoPs. PoPs are often located at Internet exchange points and colocation centres." Wikipedia
