Certified GKH Gardening Expert
I can't find a whole ot of literature on the subject, but it appears to be referring to a tree with an extra female chromosome. This would appear to make it sterile, and not drop seed.
I am not well versed in trees of your area, but your local extension would. This link can help you find the closest one to you: https://www.gardeningknowhow.com/extension-search/