Name that thing... Circular 4-pin female connector
This maybe a not very precise description:


  4 Pin Female Inline Microphone Connector: These circular connectors are
  most commonly used for microphones, but they are rugged, multi-pin
  connectors suitable for a wide variety of uses. Each connector is
  keyed to ensure proper polarity. They provide a threaded locking ring
  for reliable contact under extreme shock and vibration. These
  connectors are great for mobile use and can handle both voice, data
  and power applications. Includes a built in strain relief


According to 


http://www.vetco.net/catalog/product_info.php?products_id=6552
http://en.wikipedia.org/wiki/Microphone_connector