What is a Terraform module?

A Terraform module is fundamentally defined as a set of Terraform resources that are managed as a single unit. This encapsulation allows users to create reusable components for their infrastructure. Modules promote organization, reusability, and maintainability of Terraform configurations. By grouping related resources into modules, you can instantiate them multiple times with different parameters and configurations, thus promoting best practices in Infrastructure as Code.

In practice, a module typically consists of a directory containing one or more Terraform configuration files, which may include variables, outputs, and resource definitions. Using modules can significantly simplify complex infrastructure deployments, allowing teams to avoid redundancy and manage complicated setups more effectively.

The other options don't accurately describe what a Terraform module is: it is not an Amazon Web Services service, a coding language, or a third-party API. Each of those has distinct definitions and purposes unrelated to the concept of a module within Terraform's framework.