[FFmpeg-user] Frame types

[Steven Penny]

I have searched ffmpeg-user archives as well as Wikipedia, I am still not quite
clear on this. I have come across several terms for different frame types

  I-frame
  P-frame
  B-frame
  intra frame
  inter frame
  reference frame
  key frame

It appears that

  I-frame
  intra frame
  key frame
  reference frame

are synonymous while "inter frame" is synonymous with "non I-frame" or
"P-frame and B-frame". Is this correct? Also any canonical sources of this
information would be welcome as well.