Lists can be defined in a variable block. For example, let's say you have the following files on your Terraform server.

├── main.tf (root module)
├── data.tf
├── locals.tf
├── outputs.tf
├── providers.tf
├── terraform.tfstate
├── variables.tf
├── child (directory)
│   ├── main.tf (child module)
│   ├── data.tf
│   ├── outputs.tf
│   ├── resources.tf

For example, let's say your variables.tf file has the following.

variable "environments" {
  type = list(string)
  sensitive = false
  default = ["dev", "stage", "prod"]
}

And your outputs.tf file in the same directory as your main root module (main.tf) could then output the environments list.

output "my-environments" {
  value = var.environments
}

The terraform output command . . .

terraform output

. . . should return the following.

my-environments = tolist([
  "dev",
  "stage",
  "prod",
])

Or, you can output specific elements in the list.

output "environment-0" {
  value = var.environments[0]
}

output "environment-1" {
  value = var.environments[1]
}

output "environment-2" {
  value = var.environments[2]
}

Which should return the following.

environment-0 = "dev"
environment-1 = "stage"
environment-2 = "prod"