Technically, if someone else is having sex with your wife, then you're a cuckold. However, many people would argue that cuckolding is when there is an element of humiliation in the proceedings.
I would argue that, as soon as the husband starts to take a back seat and his role is more voyeuristic, then that is where cuckolding kicks in. For me, and in most vanilla people's minds, this scenario is already humiliating. The folks you hear on this site talking about more extreme forms of humiliation: small penis humiliation; sissification; having the husband clean up etc - these acts are extensions of simple cuckoldry. These people are exploring their own limits and deliberately 'stress testing' their own relationships and giving their women the ride of their lives.
For these men, the humiliation aspect is affirming and signifies strength of character. For most others it makes them an object of derision. Many of these guys are professionals and successful in their own fields. They have children and are respected.