The Terraform provider registry is where providers are pulled from, when you do a `terraform init`. Providers are plugins that tell TF how to talk to some cloud API, like GCP or AWS.
If you do `terraform init` in CI/CD or locally … and haven't vendored the providers … well, you're not applying Terraform right now.
This is exactly why we built outageowl.io. There is a gap between vendors and customers.