When the source of a module is a version control repository or archive file (generically, a “package”), the module itself may be in a sub-directory relative to the root of the package.
A special double-slash syntax is interpreted by Terraform to indicate that the remaining path after that point is a sub-directory within the package. For example:
hashicorp/consul/aws//modules/consul-clustergit::https://example.com/network.git//modules/vpchttps://example.com/network-module.zip//modules/vpcs3::https://s3-eu-west-1.amazonaws.com/examplecorp-terraform-modules/network.zip//modules/vpc
If the source address has arguments, such as the ref argument supported for the version control sources, the sub-directory portion must be before those arguments:
Terraform will still extract the entire package to local disk, but will read the module from the subdirectory. As a result, it is safe for a module in a sub-directory of a package to use a local path to another module as long as it is in the same package.