Cuckolding
Cuckolding is a consensual dynamic in which one partner is aroused by watching or knowing their partner is intimate with someone else, often with an element of erotic surrender.

Cuckolding is a consensual erotic dynamic in which one partner — traditionally a man — finds arousal in watching, or simply knowing, that their partner is enjoying someone else. The appeal often blends vulnerability, trust and a willing sense of surrender, and it overlaps with candaulism and the hotwife dynamic.
In practice, couples shape it to their own tastes. Some keep it to fantasy and talk; others involve a third partner, often called a bull. Rules vary widely: how much the watching partner participates, what is shared afterward, and which boundaries are firm.
Like everything in the lifestyle, cuckolding works only on a foundation of honesty and enthusiastic consent. Done well it is an expression of deep trust rather than humiliation — though couples who enjoy a lighter power element simply negotiate that openly too.
Frequently asked
Only if a couple wants it to be. For many it centres on trust, arousal and surrender rather than degradation.
The third partner invited to be intimate with the woman, within the couple's agreed boundaries.