Ambiguous definitions concerning which behaviors constitute sex, abstinence, and virginity may lead to arbitrary interpretations of meaning or miscommunication, which could be particularly problematic in health care, educational, and research contexts. The purpose of this study was to examine and compare definitions of sex, abstinence, and virginity between samples of 454 university students and 126 AASECT-certified sexuality professionals. Compared to the AASECT professionals, students were less likely to classify 10 of 11 behaviors as sex, they were more likely to indicate that oral-genital contact maintains one's virginity, and they were more likely to indicate that oral-genital contact and hand-genital contact is consistent with abstinent behavior. Relative to previous studies, these findings also suggest that conceptualizations of abstinence and the classification of oral-genital contact may be changing among young adults. Overall, the primary implication of these findings is that sexual health professionals should be mindful of the interpretative latitude afforded to individuals when using terms intended to refer to a range of sexual behaviors rather than explicitly identifying the targeted behaviors. (Contains 3 tables.)