>>512681783
There isn't a consistently-used definition. Scientists call things different species if they look different and/or occupy different parts of the world.
I can make up a definition but it's just going to be anon's bullshit on a mongolian basketweaving forum. Still, here you go: Two creatures may considered to form a single species if
(1) they can breed and produce viable offspring
(2) calculated genetic distance between them, based on DNA analysis, is less than some number