Terraform is an open-source infrastructure-as-code (IaC) tool that allows to define, provision, and manage cloud infrastructure resources using a declarative configuration language. It supports a wide range of cloud providers, including AWS, Azure, and Google Cloud, enabling the automation of resource management across different environments. Terraform tracks infrastructure state and ensures changes are applied consistently, making it easy to version control infrastructure configurations. It's widely used for creating, updating, and maintaining infrastructure in a scalable and repeatable manner.