There are competing definitions of race. Some are slang, some are scientific. Some are ambiguous and some are precise. Some are falsifiable and some exist purely on the strength of those that assert them.
Personally, I prefer the scientific, the precise, the falsifiable.
This is one particular definition, from a third-year zoology course from Olkahoma State University which I reckon is pretty good.
"Definition of Race: A race is a geographically circumscribed population or set of populations that differ from all other populations of a species.