Removing resources from state without destroying them: `removed` blocks and `terraform state rm`

Sometimes you want Terraform to stop managing an object without deleting it. Perhaps another team is taking over a database, the resource is moving to a different Terraform configuration, or it was imported by mistake. If you simply delete the resource block, Terraform will plan to destroy the real object, because state still contains it and configuration no longer does. You need a way to forget it instead.