What is a Terraform Module?

A Terraform Module is a container for multiple resources that are used together. Every directory containing Terraform files is a module. The directory you run Terraform from is the root module. Reusable modules are called child modules. Call a module: module "vpc" { source = "./modules/vpc"; region = var.region; cidr_block = "10.0.0.0/16" }. Source can be a local path, Terraform Registry path ("terraform-aws-modules/vpc/aws"), Git URL, or S3 bucket. Modules encapsulate complexity — a VPC module might create the VPC, subnets, internet gateway, route tables, and NAT gateways internally, exposing only vpc_id and subnet_ids as outputs. The Terraform Registry has hundreds of official and community modules for common infrastructure patterns.