What is the meaning of HOT-1, HOT-2, CAM, etc., in cockpit voice recorder transcripts?
They may vary from report to report, and the abbreviations used will be laid out in the report before the transcript, for flight 1549 (NTSB, .pdf) they are as follows:


  
  ATIS Radio transmission from the Automated Terminal Information System
  RDO Radio transmission from accident aircraft, US Airways 1549
  CAM Cockpit area microphone voice or sound source
  PA Voice or sound heard on the public address system channel
  HOT Hot microphone voice or sound source
  INTR Interphone communication to or from ground crew
  
  For RDO, CAM, PA, HOT and INTR comments:
  
  
  -1 Voice identified as the Captain
  -2 Voice identified as the First Officer
  -3 Voice identified as cabin crewmember
  -4 Voice identified as groundcrew
  -? Voice unidentified
  
  FWC Automated callout or sound from the Flight Warning Computer
  TCAS Automated callout or sound from the Traffic Collision Avoidance System
  PWS Automated callout or sound from the Predictive Windshear System
  GPWS Automated callout or sound from the Ground Proximity Warning System
  EGPWS Automated callout or sound from the Enhanced Ground Proximity Warning system
  RMP Radio transmission from ramp control at LaGuardia
  GND Radio transmission from ground control at LaGuardia
  CLC Radio transmission from clearance delivery at LaGuardia
  TWR Radio transmission from the Air Traffic Control Tower at LaGuardia
  DEP Radio transmission from LaGuardia departure control
  4718 Radio transmission from another airplane (Eagle flight 4718)
  CH[1234] CVR Channel identifier 1=Captain 2= First Officer 3= PA 4= Cockpit Area Microphone
  * Unintelligible word
  @ Non-Pertinent word
  &amp; Third party personal name (see note 5 below)
  # Expletive
  -, - - - Break in continuity or interruption in comment
  ( ) Questionable insertion
  [ ] Editorial insertion
  


HOT vs. CAM:


  This recording contained audio from Hot microphones used by the flightcrew. The voices or sounds on these channels were also, at times, heard by the CVR group on the CAM channel and vice versa. In these cases, comments are generally annotated as coming from the source (either HOT or CAM) from which the comment was easiest to hear and discern.