A quick google and I found this at BBA-reman.com
"A Three-Way converter is a triple purpose converter. It reduces nitrous oxides into nitrogen and oxygen. And, like the two-way converter, it oxidizes unburned harmful hydrocarbons and carbon monoxide into water and carbon dioxide."

I'm going to get it to the dealer soon, and I just thought typing Civic Hybrid in the Hybrids owned was kind of redundant. I was think it might have been sitting on the dealers lot for awhile and a fresh tank of gas would make it go away. It hasn't.