The Terraform collection type that should be used to store key/value pairs is map. A map is a collection of values that are accessed by arbitrary labels, called keys. The keys and values can be of any type, but the keys must be unique within a map. For example, var = { key1 = "value1", key2 = "value2" } is a map with two key/value pairs. Maps are useful for grouping related values together, such as configuration options or metadata. References = [Collection Types], [Map Type Constraints]

This is the command that you would use to access all of the attributes and details of a resource managed by Terraform, by providing the resource address as an argument. For example, terraform state show 'aws_instance.example' will show you all the information about the AWS instance named example.

The terraform refresh-only command is intended to detect state file drift. This command synchronizes the state file with the actual infrastructure, updating the state to reflect any changes that have occurred outside of Terraform.
From terraform plan -refresh-only:
"Use this to detectdrift, i.e., changes made outside of Terraform."
It compares actual infrastructure to what's recorded in the state file.

A module can declare a variable with a default value without requiring the caller to define it. This allows the module to provide a sensible default behavior that can be customized by the caller if needed. Reference = [Module Variables]

This is the command that can add existing resources into Terraform state, by matching them with the corresponding configuration blocks in your files.