What exactly do these defense stats mean?

[BallisticFruit 0]

So I can't seem to find where the book explains this. When using Flame Fist, part of the effect is that the target must succeed a TN 3 Fitness (Air 4, Water 1) check or become dazed. What exactly does the (Air 4, Water 1) mean? There are also plenty of other abilities that use this format. I can't seem to find where it's explained in the book.

[rcuhljr 41]

I never found the shorthand explicitly explained anywhere, but the only reasonable reading I've found is that would be a TN3 check with void, earth, or fire, but if you use the air ring it's TN 4, water TN 1.

[WHW 1,817]

Page 178, Variable Difficulties for approaches.