What feature in Terraform allows for setting default values for input variables?

The feature that allows for setting default values for input variables in Terraform is referred to as variable defaults. This capability enables you to define default values for input variables in your Terraform configuration files. When default values are specified, if a user does not provide a value for an input variable when running Terraform, the system will automatically use the defined default value instead. This feature simplifies the management of configurations by reducing the need to explicitly pass values for every variable, thus making the configuration cleaner and easier to maintain.

While variable assignment refers to the action of setting a variable's value in the context of a Terraform configuration, it does not specifically imply that default values are being utilized. Variable types provide a way to enforce the kind of data that can be assigned to a variable but do not inherently set a value. Variable constraints allow you to enforce rules about variable values, such as minimum values or value lists, but again, they do not create default values for input variables. Hence, variable defaults are the key feature for establishing default values in Terraform.