1. Most broadly, any close occurrence of different things: see also clutter; collocation; contiguity; juxtaposition.
2. The simultaneous presence of individuals in the same physical location, not necessarily engaged in face-to-face interaction with each other: see also coaction; competition; cooperation.
3. The engagement of individuals in synchronous interpersonal communication, not necessarily in the same physical location (e.g. using mobile phones) (co-present interaction).
4. In any form of mediated communication, the phenomenological sense of ‘being there’ with another person in place and/or time: see also presence.
5. In presence studies, how an individual's sense of ‘being there’ in a virtual environment is affected by the presence of others who are also inside the simulation in the form of avatars.