I see there are four terms, Zeven, Zodd, Zdifferential, Zo in Saturn tool. I am not sure that difference between Zdifferential and Zo in Saturn tool. I am using 8.31.
My understanding about Zeven and Zodd was that.
Zeven is the single ended impedance when p and n have same singles running on them. In this case each single ended signal has ground reference which is the plane under. In other words, the return path for each p and n signal is running on the ground reference which is the plane under.
Zodd is the differential impedance when p and n have opposite polarity singles running on them. In this case the reference of p line is n line. In other words the return path of p signal follows n signal which is opposite in polarity.