All of the above mentioned are standards for measuring and calibrating loudness.Â  Loudness in an audio signal is different than volume â€“ volume may be the actual scale of signal power, but loudness is how loud an audio signal is perceived, which is a combination of volume, dynamic range, and such measurements over time.Â  Because modern signal processing technology has made it possible to completely blast the loudness of a signal, certain international broadcast standards like EBU R128 and ATSC have been enacted to prevent huge variations in loudness between certain types of broadcast signals (primarily so commercials donâ€t shatter your eardrums when youâ€re watching a quiet TV program with the volume up).Â  The K-system is a system developed by legendary mastering engineer Bob Katz (who quite literally wrote the book on mastering) that requires an engineer to first calibrate their playback system to a standardized baseline (c-weighted 85db per channel for a calibrated pink noise signal).
For more info, see http://www.tcelectronic.com/loudness/loudness-explained/