5. Terraform Modules (~11%)

Modules are how Terraform configuration scales beyond one person's working directory. Everything you learned about variables and outputs in Phase 4 was secretly preparing you for this: a module is just a directory of Terraform files with a defined input/output interface, and "using modules" means wiring those interfaces together. This phase covers what a module is, where modules come from, how you call them and pass data in and out, and how to version them so a registry update doesn't silently break your infrastructure.