What are the artificial duchesses Higgins talks about? (Act 4)

Higgins complains that fashionable society is foolish;

"The dinner was worse: sitting gorging there for over an hour, with nobody but a damned fool of a fashionable woman to talk to! I tell you, Pickering, never again for me. No more artificial duchesses. The whole thing has been simple purgatory."

Higgins is referring to how they set Eliza up as an "artificial duchess" and how he is tired of the whole experience.

What Higgins means when he says Eliza is a artificial duchess is that she is a fake royal.