Definition from Wiktionary, the free dictionary
middling (not comparable)
- Of intermediate or average size, position, or quality; mediocre
- The football team is never the worst or best in its league; its position is always middling.
- 12 July 2012, Sam Adams, AV Club Ice Age: Continental Drift
- The matter of whether the world needs a fourth Ice Age movie pales beside the question of why there were three before it, but Continental Drift feels less like an extension of a theatrical franchise than an episode of a middling TV cartoon, lolling around on territory that’s already been settled.
- In fairly good health.
Derived terms 
of intermediate or average quality