In simple terms, "mean level" refers to the average or typical value of something. It gives you an idea of what's normal or standard for that particular thing.
Sentences with «mean level»
Few gender differences in mean levels of maternal or child behaviors emerged. (link.springer.com)
For boys, similarity in mean level delinquency between best friends was higher than for girls. (link.springer.com)
Very linear layouts mean level design just doesn't match up to its predecessor's. (3dsblessed.com)