In a more literal vein :

A real woman is just that, an honest-to-God existing corporeal woman, rather than the figment of your horny overactive imagination.

This is both a blessing and a curse.

• Able to provide you with love and be a willing recipient of your love, unlike the aforementioned figment.
• Often has fully seperate life, with own wants and desires that do not usually jive with yours, again, unlike the aformentioned figment.

I don't necessarily think the concept is meaningless, but then, I guess my definition of real man is not what some might think. I'd say a real woman is one who is confident in herself as a person, and whether she wears lace or denim, does so because of her own personality. Nurturing (if she wants to be) but not smothering, loving but not clinging, beautiful because she is strong...

...and yes, also a concept that tends to freak out some particularly geeky geek guys. Guess it's the whole three-dimensionality thing, or the realization that women don't look like Lara Croft (barring serious congenital defects, anyway). Generally, though, the good ones get over this fast, and make good friends or geek boyfriends.