Explain Modules

Terraform.io: "A module is a container for multiple resources that are used together. Modules can be used to create lightweight abstractions, so that you can describe your infrastructure in terms of its architecture, rather than directly in terms of physical objects."

In addition, modules are great for creating reusable Terraform code that can be shared and used not only between different repositories but even within the same repo, between different environments (like staging and production). Well-designed modules also expose a small, opinionated surface and hide implementation details.