The trinity, party responsibility, and how to try and improve the game from within

[Fevelle]

Perhaps there is a language barrier, and I'm sorry for using a word that may not be as known to people with ESL.

A norm is not an enforced rule, but is merely a typical set of behaviour adopted by the public.

From Merriam Webster:
Simple Definition of norm
norms : standards of proper or acceptable behavior
the norm : an average level of development or achievement
the norm : something (such as a behavior or way of doing something) that is usual or expected

Or here is a more detailed definition:
a principle of right action binding upon the members of a group and serving to guide, control, or regulate proper and acceptable behavior
http://www.merriam-webster.com/dictionary/norm

From the link you posted:

"Norm (n.) - an authoritative standard."

So yes, maybe it was not a wise choice to use 'norm' to refer to Healer DPS.