What does "a woman of mean understanding" mean?

In the end of the first chapter of Jane Austin's Pride and Prejudice, Mrs. Bennet is described as a "woman of mean understanding". On the Web, I found two meanings:

1. of little knowledge
2. bad temper

Can someone clarify the meaning of "mean understanding" in my context?

It means of “of common understanding”: she didn’t understand much. The OED gives:

II Inferior in rank or quality.

2a. Of persons, their rank or station: Undistinguished in position; of low degree; often opposed to noble or gentle. (Cf. common adj. ¹²).) Obs.

But the citations date up through the 19^th century, so it was not yet “obsolete” in the time of Jane Austen.

Frankly, I’m not sure I would mark it obsolete so much as literary.