[UncleMeat]

It is a problem when professional jargon makes its way into the common lexicon with a different meaning. No amount of history professors telling people that "dark ages" refers to a lack of sources will overcome the association people have in their minds today. And even the "no sources" thing is reevaluated regarding the european "dark ages" ("The Bright Ages" is a recent monograph with a fair amount of chatter pushing hard on this).

The term "dark ages" was coined by Petrarch with an explicitly negative connotation. It has never been a neutral term.

[Nomentatus]

But for a very long time historians assumed knowledge wasn't advancing during the dark ages, setting that association up. Then historians changed their minds, realizing that in some areas such as mining, technology and understanding was advancing during the period.