If it has no scientific definition, it has no scientific definition. The fact that you can't provide one is good evidence. The fact that the thing you are telling me to read says so is much better evidence.
Despite the centrality of the idea of "breeds" to animal husbandry and agriculture, no single, scientifically accepted definition of the term exists.[3]: 340 A breed is therefore not an objective or biologically verifiable classification but is instead a term of art amongst groups of breeders who share a consensus around what qualities make some members of a given species members of a nameable subset.