non-emergency question about differences between chicken illnesses

[fallenweeble]

i've been reading old posts, trying to educate myself about chicken health, feeding, etc. etc.
one thing i've become a bit befuddled about is what the following terms mean:
CRD, MG, and Coryza
are these three ways to describe the same illness or does each term describe a distinct malady?

thanks!

 

[dlhunicorn]

CRD is synonymous with MG .... Coryza is a separate entity.