It means out of 600 domain extensions (endings), that many percentage of endings were registered using the same name. The more endings were registered with the same name, the more popular that name is.
Hope that makes sense
Hope that makes sense
It doesn’t make sense without an explanation.
It seems "domain ending" might be a somewhat common way to describe a TLD in lay terms. That said, I am a geek and a curmudgeon, so I still think writing out top-level domain makes the most sense in such a context.