The verbal section of the SAT exam includes a section on critical reading. Reading “critically” means reading without simply accepting the text as fact. When you read a text critically, you are trying to evaluate the validity of the claims presented, recognizing that the author necessarily has experiences, biases, or prejudices that influence his or her views on the subject.
If the piece presented is an argument, the author's biases may influence the choice of material presented or excluded, and the relative importance accorded to each claim in the construction of the overall argument. Ultimately, you have to try as far as possible to separate the author's biases from the objective merits of the claim.