Discusses definitions of sex as an S variable and as a stimulus variable. The term "gender" is introduced for those characteristics and traits socioculturally considered appropriate to males and females. The rationale for this addition to the psychological vocabulary is that the term "sex" implies biological mechanisms. Differences between females and males that are merely descriptive are frequently assumed to have biological origins. The present terminology facilitates biologically determinist models of sex differences which make it less likely that environmental sources of such differences will be explored. Sex differences in cerebral laterality are examined to illustrate this process. In contrast, research on gender is more concerned with the sociocultural factors that contribute to sex differences. Differential use of the term sex indicates different paradigms for the examination of sex differences, and psychological terminology should reflect this distinction. (55 ref) (PsycINFO Database Record (c) 2012 APA, all rights reserved)