Defining a kind is easy. A kind is one of the original sets of creatures created by God as depicted in Genesis from a creationist perspective.
easy....no problem
In fact, it is the disingenuinity of evos to claim that the concept of kind is undefined that makes someone like me think very, very poorly of evos.
Now, if you are talking about defining in scientific terms, I'd say that sort of like asking an evo to define "random", the first organism, or "species."