Please answer a question about the following article about Race (human categorization):

There is a wide consensus that the racial categories that are common in everyday usage are socially constructed, and that racial groups cannot be biologically defined. Nonetheless, some scholars argue that racial categories obviously correlate with biological traits (e.g. phenotype) to some degree, and that certain genetic markers have varying frequencies among human populations, some of which correspond more or less to traditional racial groupings. For this reason, there is no current consensus about whether racial categories can be considered to have significance for understanding human genetic variation.

What type of group can't be biologically defined?
racial