The file:/// scheme allows a user to "fetch" data from their own computer’s storage as if it were a remote server. This is useful for testing scripts locally or automating tasks that involve reading local system files. Standard: curl file:///etc/passwd

That seems to represent a URI scheme like curl-url-file:/// (perhaps a custom or pseudo-protocol for some tool or script).

In cURL, file:/// is used to read from the local filesystem.