Cloud resource tagging is the practice of attaching metadata key-value pairs to cloud infrastructure resources across AWS, Azure, and GCP to organize, track, and allocate costs at scale. Effective tagging enables accurate cost attribution to teams, projects, and business units while supporting governance, automation, security access control, and compliance auditing. Tags (or labels in GCP) serve as the foundation for chargeback/showback models, budget tracking, anomaly detection, and resource lifecycle management. Understanding tagging taxonomy design, enforcement mechanisms, and automation strategies transforms cloud cost visibility from opaque to transparent, enabling FinOps teams to optimize spending with granular insights into who is using what, when, and why.