Difference between kernel f and isotrope vectors

[kthouz]

i have a problem in differenciating kernel f and isotrope vectors,if someone could explain me,....

 

[HallsofIvy]

The "kernel" of f is the set of vectors x such that f(x)= 0. But I have no idea what you mean by "isotrope" vectors. I tried googling on it and got "isotropic" vectors instead- which have to do with quantum mechanics.