Bias is a disproportionate weight in favor of or against an idea or thing, usually in a way that is inaccurate, closed-minded, prejudicial, or unfair. Biases can be innate or learned. People may develop biases for or against an individual, a group, or a belief. In science and engineering, a bias is a systematic error. Statistical bias results from an unfair sampling of a population, or from an estimation process that does not give accurate results on average.

Prejudice can be an affective feeling towards a person based on their perceived group membership. The word is often used to refer to a preconceived evaluation or classification of another person based on that person's perceived personal characteristics, such as political affiliation, sex, gender, gender identity, beliefs, values, social class, age, disability, religion, sexuality, race, ethnicity, language, nationality, culture, complexion, beauty, height, body weight, occupation, wealth, education, criminality, sport-team affiliation, music tastes or other perceived characteristics.