ABSTRACT The goal of this study was to explore the sexual activities that older adults consider as having had sex and to examine correlates of the ways that older men and women define sex. A sample of 286 men and women aged 60 years and older who were involved in a romantic relationship were recruited online from Prolific and Facebook advertisements. Participants were presented a list of 19 different sexual activities and asked whether they would think they had sex if they engaged in each one of those activities. Results showed that penetrative sexual activities were found to be the most likely endorsed as having had sex, followed by genital non-penetrative activities, masturbation activities, and non-genital contact. Greater sexual frequency for a sexual activity was associated with endorsing that same activity as having had sex. A cluster analysis revealed five different groups of individuals based on the activities that they considered as having had sex. Only small differences in sexual wellbeing were found among these groups of individuals. The way older men and women define sex is complex and shows great variability. Our results have important implications for the operationalization and assessment of sexual activity. Other implications for healthcare and future research are discussed.