Terraform is an open-source Infrastructure as Code (IaC) tool developed by Hashicorp that enables users to provision infrastructure in a simple, efficient, and declarative manner through repeatable code. It has a cloud-agnostic nature, allowing deployment of infrastructure to any cloud environment or on-premises environments. Terraform's architecture consists of the Terraform Core, Providers, and State file. The workflow involves defining resources in configuration files, initializing the working directory, reviewing the execution plan, applying changes, and inspecting the state of infrastructure.