A sexual group activity with 3 participants. Often consisting of two people of one gender and one person of another, but all sorts of combinations of 3 people can have have a threesome.
Sexual activities are only limited to what is consented between participants. One will sometimes see things like double penetration as one of the activities that are popular in threesomes as that requires two people to focus on one.
Sometimes people will ask for FFM, FMF, MFM or MMF in relation to a threesome. This indicates in what kind of configuration a threesome is wanted or being had. The middle letter is the gender of the person considered to be the "focus" of the threesome. So there can be a threesome with two males focusing on the single female (MFM), but also a male and female couple focusing on a single female (FFM). There notations are very binary, but are commonly found to indicate genital preferences (rather than gender preferences) for people engaging in a threesome.
