1) The general meaning of these terms in measurement technique seems self-explanatory in my opinion, in this case the exact instrument characteristic (e.g. time constants and rectifier behaviour) is specified in standards for noise emission measurements. They should be discussed also in the respective professional/scientific literature and manuals of similar professional instruments.
2) As the name suggests, it's an AC output for the amplified microphone signal, most likely modified by the gain setting and possibly a selected (A or C) "weigthing" filter. Connect an oscilloscope or audio spectrum analyzer and see.