What is a data source in Terraform?

A data source in Terraform serves as a read-only reference to information that is not directly managed by Terraform itself. This allows Terraform to access and incorporate external data into its plans and configurations. For instance, you can use data sources to retrieve information about existing infrastructure, such as the current state of certain cloud resources, without Terraform needing to control those resources.

By utilizing data sources, you can fetch details such as images from a public repository, the latest version of a cloud provider's resource, or configuration details from a different environment or service. This capability enhances the flexibility of Terraform code, enabling it to adapt based on existing structures within the infrastructure.

The other options do not accurately describe the function of a data source. A managed resource within your infrastructure typically implies that Terraform creates, updates, or deletes the resource, which is fundamentally different from the passively accessed nature of data sources. A write-only reference does not align with how Terraform operates, as data sources are solely concerned with retrieving data rather than modifying it. Lastly, while an API endpoint may be involved in the retrieval process, it is not the defining characteristic of a data source in Terraform; the focus is on accessing read-only information.