When two or more unwilling individuals are forced to participate in sexual acts with each other.
This might be because of being Bound Together by restraints, being coerced, or because of being under (apparent) duress, such as being held At Gunpoint or other Threats.
If any (but not all) of the participants are willing, you should probably use the Rape tag instead.
Avoid using this tag when the participants are merely under Hypnosis or Mind Control, unless their powerless "inner selves" are also portrayed witnessing the scene.