speaker efficiencey?? Starting point...? 92db??

I recently purchased an spl meter to map out the response on my HT system. The manual for my Yamaha Rx1500(using as pre/pro) says to start at 0 db volume and test each channel from the listening position to 75db. I went through each channel(7.1 sys) and at 0 db i only had to adjust the left front and right surround speakers slightly to hit the 75. All other channels hit 75db at 0db.

Iam guessing that it would be correct to say that my requency response is relatively flat. Forgive my ignorance but i am just starting out in this crazy world of HT. My speakers have an efficiency rating to 92db. what exactly does the efficiency rating mean?>??