System.pid
You're seeing just the function
pid, go back to System module for more information.
Specs
pid() :: String.t()
Returns the operating system PID for the current Erlang runtime system instance.
Returns a string containing the (usually) numerical identifier for a process.
On Unix-like operating systems, this is typically the return value of the getpid() system call.
On Windows, the process ID as returned by the GetCurrentProcessId() system
call is used.
Examples
System.pid()