What does the 'terraform refresh' command do?

The 'terraform refresh' command is designed to update the Terraform state file with the current state of the infrastructure as it exists in the real world. This means that Terraform queries the provider and gathers real-time data about the resources that it manages, reflecting any changes that may have occurred since the last time the state file was updated.

This command is particularly useful in scenarios where manual changes were made to the infrastructure outside of Terraform, such as through a cloud provider’s console or API. By running 'terraform refresh', users ensure that Terraform’s understanding of the infrastructure is accurate and up to date, which is crucial for any subsequent operations, like planning or applying changes.

The other options relate to Terraform functionality but do not accurately represent what 'terraform refresh' does. For instance, applying changes to the infrastructure involves the 'terraform apply' command, while reverting changes relates to managing resources differently, and cleaning up unused resources does not apply directly to this command's purpose. Each of these functions serves a different role within Terraform's workflow, emphasizing the specific nature of the 'refresh' command.