What term refers to a fixed or distorted generalization about all members of a particular group?

The correct term that describes a fixed or distorted generalization about all members of a particular group is "stereotypes." Stereotypes simplify complex human traits and behaviors by attributing specific characteristics to entire groups, often leading to misleading or overly simplistic views. This can occur in various social contexts and can be based on aspects like race, gender, age, religion, or nationality.

In contrast, discrimination involves actions or behaviors that treat people unfairly based on their group identity, while prejudice refers to preconceived opinions or feelings, often negative, towards a group without sufficient knowledge or reason. Ethnocentrism is the belief in the superiority of one’s own culture over others, which can influence how groups are stereotyped but is distinct from the broader concept of stereotypes themselves. Thus, the choice of "stereotypes" is the most accurate representation of the concept described in the question.