The phrase describes a feature within Facebook, specifically related to video content. It indicates the presence of individuals who are currently watching the same video as the user. For example, if a user is watching a live stream, Facebook might display a message indicating “5 other viewers” are also watching. This provides immediate social context.
Knowing how many, and sometimes who, is watching a shared video enhances the viewing experience, creating a sense of community and shared activity. This feature draws from earlier trends in online interaction, such as chat rooms and instant messaging, that emphasized the real-time presence and interaction of multiple users. The ability to see the presence of other users has been shown to increase engagement and encourage longer viewing sessions.