Terraform is HashiCorp's open-source infrastructure as code (IaC) tool that provisions and manages cloud and on-premises resources using declarative configuration files written in HashiCorp Configuration Language (HCL). It works by building a dependency graph of your infrastructure, determining the optimal execution order, and applying changes through provider-specific APIs to AWS, Azure, GCP, Kubernetes, and hundreds of other platforms. Understanding Terraform's workflow—write configuration, initialize providers, plan changes, apply infrastructure—is essential, but the real power lies in mastering state management, modules, and meta-arguments that enable you to build scalable, maintainable infrastructure with minimal manual intervention.