Back in early 2010, I did a Y-12 test on my second cousin via the Genographic Project. Soon thereafter, I transferred the results over to FTDNA and he had zero matches at the Y-12 level.
Now, all these years later, I finally had a chance to test his father (my first cousin, once removed). For his Father, I did a Y-111 test and a Big-Y. The Father has plenty of Big-Y matches, but for his Y-STR, he only has one match and it's at the Y-12 level: his own son who I tested in 2010!
What is the significance of such a staggering lack of STR matches? What does that mean in simple terms that I can explain to them?
For what it's worth, I also did a Family Finder test on the Father and there are a respectable number of matches, just as there are for his Big-Y. It's only the Y-STR matches which are remarkably vacant.