This document provides an overview of data centers, including their definition, key components, complexity, and tier classifications. A data center is a facility that houses computing infrastructure for data processing, communication, and storage. It typically contains servers, storage, networking equipment, and other components. Data centers can range from small facilities with under 100 servers to massive operations with over a million servers. They involve significant physical and technological resources to provide processing services. The document discusses some of the largest data centers in terms of server count and gives examples of core data center components. It also touches on other important considerations like facilities, energy usage, and processes involved in data center design and operation.