Data Center Tiers are a classification system that defines the reliability and performance of data centers. There are four main tiers, ranging from Tier I to Tier IV. Each tier indicates the level of redundancy, uptime, and fault tolerance, with Tier I being the most basic and Tier IV offering the highest level of reliability. A Tier I data center has no redundancy and is susceptible to outages, while a Tier IV data center includes multiple active power and cooling paths, ensuring continuous operation even during failures. This tiered system helps businesses choose the right data center based on their specific needs and budget.