Adata center is a climate-controlled building or set of buildings that houses the that store and deliver mission-critical information and services.

A data center is a climate-controlled building or set of buildings that house the servers that store and deliver mission-critical information and services.
A data center will serves as some sort of main response giver that will cause a reaction to the request made by the client (user). Since it's tend to be overloaded with data, it often stored on a very cold room