In a threesome, either two women and a man or two men and a woman have sex with each other.
As the name suggests, a threesome is sex with three people. It doesn't matter whether two women sleep with one man or two men with one woman. The term remains the same.
Accordingly, anyone who says they have had a threesome is not yet making a statement about which sexes were involved. Interestingly, however, group sex with three people of the same sex is clearly less often described as a "threesome".
Among other things, threesomes also play an important role in porn. Men in particular are always told that this is an absolute pipe dream for them. Some men, however, have a lot of respect for having to satisfy two women at the same time. One thing is certain: even if this kind of sex exerts a special fascination on many, some realise in retrospect that films and stories often raise expectations that cannot be fulfilled in the end.
Nowadays, those who want to have a threesome usually find what they are looking for in relevant chats, but also in swingers' clubs. Especially in connection with the corresponding clubs or locations, like-minded people meet again and again who are looking for a quick adventure in a threesome.
Incidentally, a variation of the classic threesome is when one individual decides to "only" watch the other two. In this case, voyeuristic urges are essentially satisfied.