It is impossible to draw a clear line between races, but it is also impossible to draw a clear line between colors of the visual spectrum, and yet "red" and "blue" exist. For a non-IQ related example, people of Ashkenazim heritage are known to be at risk for certain genetic issues, while people of African heritage are known to be exposed to heart-related risks.

The concept of race (or any other word that symbolizes this concept) is statistically significant and useful - more so in countries that are much more homogeneous than the USA.