Explanation
Some backends support state locking, which prevents other users from modifying the state file while a Terraform operation is in progress. This prevents conflicts and data loss. Not all backends support this feature, and you can check the documentation for each backend type to see if it does.

This is a key benefit of the Terraform state file, as it stores and tracks the metadata and attributes of the resources that are managed by Terraform, and allows Terraform to compare the current state with the desired state expressed by your configuration files.

Explanation
This will trigger a run in the Terraform Cloud workspace, which will perform a plan and apply operation on the infrastructure defined by the Terraform configuration files in the VCS repository.

Explanation
This is how Terraform chooses which version of the provider to use, when you add a new resource to an existing Terraform configuration, but do not update the version constraint in the configuration. The lock file records the exact version of each provider that was installed in your working directory, and ensures that Terraform will always use the same provider versions until you run terraform init -upgrade to update them.