Which term describes preconceived opinions that are not based on reason?

The correct term for preconceived opinions that are not based on reason is "prejudices." Prejudice refers to a preconceived judgment or opinion about an individual or a group, often based on characteristics such as race, ethnicity, religion, gender, or other factors, without a fair or rational evaluation of the facts. This term emphasizes the irrationality and lack of evidence that typically accompanies such opinions, which can lead to unfair attitudes and behaviors towards others.

In contrast, bias generally refers to an inclination or preference that affects impartial judgment. While bias can play a role in forming prejudices, it does not specifically capture the non-rational aspect central to prejudices. Discrimination involves actions or behaviors that treat people unfairly based on prejudicial beliefs, making it the operational outcome of prejudices rather than the belief itself. Stereotypes, while also related, refer to oversimplified and generalized beliefs or ideas about a group, which may or may not include the element of unreasonable judgment found in prejudices. Thus, the focus on irrationality and lack of evidence makes "prejudices" the best descriptor for the question asked.