Unless you're into reading Middle English poetry, or tend to spend time on Twitter criticising people of a liberal persuasion, the chances are you've probably never heard the word 'cuckold'.
It's an old English word that is used to describe a man who is married to an unfaithful wife - it can also be the act of another man making a husband a cuckold by sleeping with his wife.
Anyway, it comes from a bird - the cuckoo - which has a habit of laying eggs in other bird's nests, but it is also a sexual trend that is growing in popularity worldwide.
It basically involves three people; a husband, a wife, and another bloke. The husband is not actually part of the sex though. They just watch the other guy have sex with their wife. Sometimes they ask to be tied up, sometimes they get humiliated, and sometimes they are ordered around by the other two.
There are special names, of course. The 'cuck' is the husband that watches the action whereas the 'bull' is the guy in charge of proceedings.
Obviously - like all of these sorts of things - it's not for everyone, but according to Google Trends searches for 'cuckold' are on the up and up. It outstripped searches for the usually popular 'threesome' this January.
As you have probably guessed, the internet is the place to be to get involved with this sort of action. You'll need to scour for some of the more specialist forums out there to find like-minded people, but they are out there.
The Metro sought out some stories from those in the know; here are some of the best bits.
Harry (we presume not his real name) from London said: "I enjoy being the man invited to please a wife in front of her hubby. A few days ago, I visited a couple and was there for several hours.
"The husband was ordered to make us coffee and cheese toasties, but I also gave him sexual orders. This particular husband is bisexual and will watch, as well as give me oral sex. He especially likes the humiliation of seeing his wife enjoy sex with another man.
"Sometimes, he'll also be allowed to have sex with her."
Well, the coffee and cheese toasties sound good, at least.
Elliot (you get the picture with regards to his name) also from London said: "I enjoy humiliating the men. I'll make the husband bring me beer, and then I'll proceed to drink it with his wife sitting on my lap.
"Sex-wise though, it's about sating the wife's need for a proper man. The cuck is always banished from the room.
"If he is good, I get the wife to call him in. The husbands seem to get off on being bested and are usually the ones to arrange the play session."
Each to their own, I guess. Or not, as the case may be.
Featured Image Credit: 20th Century Fox