GenServer.handle_info

You're seeing just the callback handle_info, go back to GenServer module for more information.
Link to this callback

handle_info(msg, state)

View Source (optional)

Specs

handle_info(msg :: :timeout | term(), state :: term()) ::
  {:noreply, new_state}
  | {:noreply, new_state, timeout() | :hibernate | {:continue, term()}}
  | {:stop, reason :: term(), new_state}
when new_state: term()

Invoked to handle all other messages.

msg is the message and state is the current state of the GenServer. When a timeout occurs the message is :timeout.

Return values are the same as handle_cast/2.

This callback is optional. If one is not implemented, the received message will be logged.