Stereotypes are mental concepts held of particular social groups that are ascribed a set of characteristics and are perceived as being fairly homogenous (Braithwaite, Lynd-Stevenson, & Pigram, 2003).
Braithwaite, V., Lynd-Stevenson, R., & Pigram, D. (1993). An empirical study of ageism: From polemics to scientific utility. Australian Psychologist, 28, 9-15.