When declaring a Terraform output, the value argument is required. Outputs are a way to extract information from Terraform-managed infrastructure, and the value argument specifies what data will be outputted. While other arguments like description and sensitive can provide additional context or security around the output, value is the only mandatory argument needed to define an output.
References = The requirement of the value argument for outputs is specified in Terraform's official documentation, which provides guidelines on defining and using outputs in Terraform configurations.

Explanation
The terraform state list command lists all resources that are managed by Terraform in the current state file1. The terraform state show command shows the attributes of a single resource in the state file2. By using these two commands, you can compare the VM IDs in your list with the ones in the state file and identify which one is managed by Terraform.

Comprehensive and Detailed in-Depth Explanation:The terraform init command is required before using a new backend or integrating with HCP Terraform/Terraform Cloud.
* terraform init initializes the working directory and sets up the backend, downloading necessary provider plugins and modules.
* If the backend configuration changes, Terraform willrequirere-initialization to apply those changes.
* Without running terraform init, Terraform willfailto use a new backend or remote Terraform Cloud workspace.
Official Terraform Documentation Reference:terraform init - HashiCorp Documentation

The terraform state file is locked when a Terraform operation that could write state is in progress. This prevents concurrent state operations that could corrupt the state. The forbidden actions when the state file is locked are those that could write state, such as terraform apply, terraform destroy, terraform refresh, terraform taint, terraform untaint, terraform import, and terraform state *. The terraform validate command is also forbidden, because it requires an initialized working directory with the state file. The allowed actions when the state file is locked are those that only read state, such as terraform plan, terraform show, terraform output, and terraform console.
References = [State Locking] and [Command: validate]

These are features of Terraform Cloud, which is a hosted service that provides a web-based UI, remote state storage, remote operations, collaboration features, and more for managing your Terraform infrastructure.