Bias is a tendency to believe that some people, ideas, etc., are better than others, which often results in treating some people unfairly.
Example: If someone is biased toward women, they might hire only women because they feel they make better employees for some gender-related reason. Conversely, if someone is biased against women, they might hire a man over a more-qualified female candidate.
If there is bias in a resource that you are reading, then it is not a reliable source. Below are a few examples of other types of bias:
Explicit bias refers to attitudes and beliefs (positive or negative) that we consciously or deliberately hold and express about a person or group. Explicit and implicit biases can sometimes contradict each other.
Implicit bias includes attitudes and beliefs (positive or negative) about other people, ideas, issues, or institutions that occur outside of our conscious awareness and control, which affect our opinions and behavior. Everyone has implicit biases—even people who try to remain objective (e.g., judges and journalists)—that they have developed over a lifetime. However, people can work to combat and change these biases.
Confirmation bias is our subconscious tendency to seek and interpret information and other evidence in ways that affirm our existing beliefs, ideas, expectations, and/or hypotheses. Therefore, confirmation bias is both affected by and feeds our implicit biases. It can be most entrenched around beliefs and ideas that we are strongly attached to or that provoke a strong emotional response.