Reference: https://docs.aws.amazon.com/cloudformation-cli/latest/userguide/resource-types.html

Sentinel is an embedded policy-as-code framework integrated with the HashiCorp Enterprise products. It enables fine-grained, logic-based policy decisions, and can be extended to use information from external sources.
Using Sentinel with Terraform Cloud involves:
* Defining the policies - Policies are defined using the policy language with imports for parsing the Terraform plan, state and configuration.
* Managing policies for organizations - Users with permission to manage policies can add policies to their organization by configuring VCS integration or uploading policy sets through the API. They also define which workspaces the policy sets are checked against during runs. (More about permissions.)
* Enforcing policy checks on runs - Policies are checked when a run is performed, after the terraform plan but before it can be confirmed or the terraform apply is executed.
* Mocking Sentinel Terraform data - Terraform Cloud provides the ability to generate mock data for any run within a workspace. This data can be used with the Sentinel CLI to test policies before deployment.
https://www.terraform.io/docs/cloud/sentinel/index.html

Software development encourages code reuse through reusable artifacts, such as libraries, packages and modules. Most programming languages enable developers to package and publish these reusable components and make them available on a registry or feed. For example, Python has Python Package Index and PowerShell has PowerShell Gallery.
For Terraform users, the Terraform Registry enables the distribution of Terraform modules, which are reusable configurations. The Terraform Registry acts as a centralized repository for module sharing, making modules easier to discover and reuse.
The Registry is available in two variants:
* Public Registry houses official Terraform providers -- which are services that interact with an API to expose and manage a specific resource -- and community-contributed modules.
* Private Registry is available as part of the Terraform Cloud, and can host modules internally within an organization.
https://www.terraform.io/docs/registry/index.html

To upgrade to the latest acceptable version of each provider, run terraform init -upgrade. This command also upgrades to the latest versions of all Terraform modules.
https://www.terraform.io/docs/configuration/providers.html