"set of animals or plants in which the members have similar characteristics to each other and can breed with each other"
Breeding is a criteria for differentiating species and also there is a lot of difference between theory and practice.
“Can interbreed” is a fuzzy line too, the probability decreases as genetic distance increases but it doesn’t just suddenly stop. Sometimes very different species can interbreed, and sometimes a small change is enough to make it stop working. Of course, often breeding can be accomplished with human intervention, but never in nature, for simple mechanical or behavioral reasons.