You're joking, right? :D

Honestly, if you held a gun to my head, I could not give you a definition of the word. I have looked for definitions, but they're very vague and contradictory.

From usage, it seems to mean "a powerful and sinister force that oppresses women".

Nope. The way feminist use Patriarchy reminds me of creationist (and IDers) use of God, miracles, and the supernatural.