What is cuckold husband?

A husband is a man who is married. A cuckold is a married man whose wife/partner is sexually active another man (or other men). The adding of "husband" to cuckold is reundant, strictly speaking, as all cuckolds are husbands. However, in contemporary usage, cuckolding is also a BDSM feitsh in which one partner gets a masochistic thrill from the other partner's "non-monogamy." In this feitsh the "cuckold" need not be married, so the term "cuckold husband" is sometimes used to indicate the marital bond.