The reason why creationists aren't more upfront about what a kind is is that kind has to mean something other than species, otherwise you have millions of animals to fit on Noah's Ark. However, the biblical passages that refer to kinds ("after their kind"), seem to be referring to the ability of given animals to reproduce. In science this principle is known as the biological species concept, and this is used to define what a species is.
Note that the biological species concept has so many exceptions to it with the ability of animals to hybridize and the fact that it only works for sexual reproduction which can't be used to distinguish bacteria that in the next decade or two this rule of thumb will likely be replaced by a genetic standard. It is these exceptions that creationists use to argue that they aren't talking about a species, but they really are. All but the rarest of hybrids are sterile and cannot reproduce, so most of these exceptions end at the first generation.
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