What sexual behavior is considered promiscuous varies between cultures, as does the prevalence of promiscuity. Different standards are often applied to different genders and civil statuses. Feminists have traditionally argued a significant double standard exists between how men and women are judged for promiscuity. Historically, stereotypes of the promiscuous woman have tended to be negative, such as "the slut" or "the harlot", while male stereotypes have been more varied, some expressing approval, such as "the stud" or "the player", while others imply societal deviance, such as "the womanizer" or "the philanderer". A scientific study published in 2005 found that promiscuous men and women are judged equally harshly. However, later studies show evidence for a double standard.
Promiscuity is common in many animal species. Some species have promiscuous mating systems, ranging from polyandry and polygyny to mating systems with no stable relationships where mating between two individuals is a one-time event. Many species form stable pair bonds, but still mate with other individuals outside the pair. In biology, incidents of promiscuity in species that form pair bonds are usually called extra-pair copulations.
Accurately assessing people's sexual behavior is difficult, since strong social and personal motivations occur, depending on social sanctions and taboos, for either minimizing or exaggerating reported sexual activity.
American experiments in 1978 and 1982 found the great majority of men were willing to have sex with women they did not know, of average attractiveness, who propositioned them. No woman, by contrast, agreed to such propositions from men of average attractiveness. While men were in general comfortable with the requests, regardless of their willingness ("Why do we have to wait until tonight?", ", I'm married"), women responded with shock and disgust ("You've got to be kidding", "What is wrong with you? Leave me alone").
The number of sexual partners people have had in their lifetimes varies widely within a population. A 2007 nationwide survey in the United States found the median number of female sexual partners reported by men was seven and the median number of male partners reported by women was four. The men possibly exaggerated their reported number of partners, women reported a number lower than the actual number, or a minority of women had a sufficiently larger number than most other women to create a mean significantly higher than the median, or all of the above (see Pareto principle). About 29% of men and 9% of women reported to have had more than 15 sexual partners in their lifetimes. Studies of the spread of sexually transmitted diseases consistently demonstrate a small percentage of the studied population has more partners than the average man or woman, and a smaller number of people have fewer than the statistical average. An important question in the epidemiology of sexually transmitted infections is whether or not these groups copulate mostly at random (with sexual partners from throughout a population) or within their social groups (assortative mixing).