More Info - Cuckoldry as a fetish - Not so much wife swapping - more like wife sharing

The term has acquired additional meanings within certain sub-cultures, referring to couples wherein the female is dominant and she takes on additional partners, while the male takes on a submissive role where he is monogamous to her, or only becoming involved sexually when it is felt to be emotionally supportive of her and her lover, or remaining altogether chaste.

The wife who enjoys cuckoldry is sometimes referred to as a hotwife. In a broader context, the contrast between a cuckold and the additional male participant (sometimes called a "stud" or "bull") is sometimes used to summarize an individuals personality or behaviour and the variability commonly seen in male libidos; the cuckold or beta male suggesting a lack of virility, perhaps sometimes having a small penis, impotence, infertility, vulnerability, weakness, or even anxiety and the stud or alpha male representing virility, potency, a larger phallus, fertility, dynamism, masculinity, strength and a sense of confidence in the ease with which he may sexually possess another man's wife. There are some who consider the use of the term "bull" to be offensive, and this term is also not used commonly in the BDSM community. Interestingly, the more virile male was once almost exclusively referred to as a "stud"; using an equine connotation rather than the bovine one of a "bull".

Cuckolding among female-dominant couples differs from the original definition of cuckolding in that many of these men are voluntarily "cuckolded" by their wives, sometimes as part of the husband's sexual fantasy and sometimes because they gain genuine sexual arousal through being humiliated by his wife being better sexually fulfilled with a potentially superior male.In some cases the husband may instigate and nurture his wife's sexual infidelity, raising the question of who is truly the dominant partner. This is a common theme in letters to erotica magazines and online sites which focus on cuckoldry.

In most modern cases of fantasy "cuckolding" the husband usually finds pleasure through that of his wife (or what he perceives to be her pleasure), and they (the wife and extra-marital participant) may both enjoy attempting to actively include him in the act of cuckolding as much as possible through serving her. Some common themes include praising her appearance, attempting to stimulate her sexually at the same time as the additional participant, and generally being engrossed in her enjoyment, usually while masturbating or involving himself in some sexual act with his wife during their activity.

Some less-common themes might include grooming his wife for her "date", homemaking, or oral sex following the conclusion of sex with the other man. When this oral sex follows ejaculation, it is termed a creampie or cleaning up.
http://encyclopedia.thefreedictionary.com/cuckold