In a cuckold marriage, the wife is completely transformed into a liberated woman who can experience as many men and as much sex as she desires. She can be confident in the knowledge that her husband is waiting faithfully for her at home and eagerly anticipating her arrival from her dates. She also knows that he no longer expects sexual pleasure from her even though he may desire it very much. He is still completely satisfied by her experiences and sexual growth as she learns more about how to please herself freely.
Another trait of the cuckold marriage is that the male partner agrees that he will not pursue any extramarital sex at all. This is strictly a freedom granted to the wife. This is why many people tend to associate female dominated marriages with the cuckold lifestyle and there is, indeed, crossover. However, in many instances the husband is simply more aroused by his wife's own experiences and transformation into the ideal "slut" than he is in his own pursuits.
Some cuckold marriages go even farther by adding the concept of pregnancy by the wife's lover to the experience. Some couples plan on the wife becoming pregnant by her lover from the very start. Others gradually grow to this level over time as both partners discover that the idea is very exciting to them and in many ways practical. This is the strongest and deepest expression of the cuckold marriage possible.
source: Cuckold Marriage