Please Explain Lane Splitting

Recently, someone complained about Sport Motorcycles passing him in a no passing zone at 25 MPH over the speed limit, and someone said that only a stupid state would not allow Lane Splitting. Please do NOT rag on STUPID motorcycle drivers in this post. I want to know about this Lane Splitting thing. Are there really states that allow vehicles to pass on 2 lane roads with oncoming traffic, and it is the responsibility of that oncoming traffic (and the car(s) being passed) to all pull over to allow that passing????? That sounds plain stupid to me. Comments!