Eine vereinfachende, typisierende Voreinstellung gegenüber einer Person oder Situation.

1922
For the most part we define first, and then see. In the great blooming, buzzing confusion of the outer·world we pick out what our culture has already defined for us, and we tend to perceive that which we have picked out in the form stereotyped for us by our culture. […]
The subtlest and most pervasive of all influences are those which create and maintain the repertory of stereotypes. We are told about the world before we see it.·We imagine most things before we experience them. And those preconceptions, unless education has made us acutely aware, govern deeply the whole process of perception. They mark out certain objects as familiar or strange, emphasizing the difference, so that the slightly familiar is seen as very familiar, and the somewhat strange sharply alien. […]
A stereotype may be so consistently and authoritatively transmitted in each generation from parent to child that it seems almost like a biological fact.
Water Lippmann: Public Opinion (1922), New Brunswick 1991, S. 81; 89f.; 93.

1935
Attitudes which result in gross oversimplifications of experience and in prejudgments are of great importance in social Psychology […]. They are commonly called biases, prejudices, or stereotypes. The latter term is less normative, and therefore on the whole to be preferred.
Gordon W. Allport: Attitudes, in: Carl Murchison (Hg.): Handbook of Social Psychology, Worcester 1935, S. 798-844, hier S. 809.

1935
A stereotype is a fixed impression, which conforms very little to the facts it pretends to represent, and results from our defining first and observing second. […] In general, public attitudes represent a more complete form of stereotype than private attitudes. […]
Racial prejudice is […] a generalized set of stereotypes of a high degree of consistency which includes emotional responses to race names, a belief in typical characteristics associated with race names, and an evaluation of such typical traits.
Daniel Katz und Kenneth W. Braly: Racial prejudice and racial stereotypes, in: The Journal of Abnormal and Social Psychology 30 (1935), S. 175-193, hier S. 181; 191f.

1948
The concept of stereotype […] refers to two different things. (1) It may refer to a tendency for a given belief to be widespread in a society. This is a sociological and statistical concept and can be illustrated by the studies that count the number of people who believe, for example, that blondes are less intellectual than brunettes or that workers are more honest than capitalists. (2) The concept may refer to a tendency for a belief to be oversimplified in content and unresponsive to the objective facts. This is a psychological concept.
David Krech und Richard S. Crutchfield: Theory and Problems of Social Psychology, New York 1948, S. 171.

1981
Clear stereotypes emerged for six ethnic groups; all were relatively positive except one, whites, which was extremely negative. The most favorable stereotypes were of Chinese and Jews. The stereotype of blacks ranked third in favorableness, followed by Italians and Germans.
Linda A. Foley and Peter L. Kranz: Black stereotypes of other ethnic groups, in: The Journal of Mind and Behavior 2 (1981), S. 435-441, hier S. 435.