Well, that's a new one on me, so, for the similarly uneducated...I very much like to see my partner as we fuck, but if you find it too vanilla, you can once your partner is in you, close your legs and have him straddle your legs in a reverse pronbone kind of way. Really is amazing
Here's a more detailed breakdown:
Prone: This term refers to the anatomical position of lying face down.
Bone: In this context, "bone" is not a literal part of the body, but rather slang for a penis or penis-related activity.
Prone-bone (slang): This term combines the two to describe the sex position where someone is sexually penetrated while they are lying face down.