Is the representation of the partner(s)’ cognitive state, namely inferences an individual make about his/her partners’ intents/understanding/purposes/goals.

This definition was taken from: Nicolas Nova, Pierre Dillenbourg, Thomas Wehrle, Jeremy Goslin, Yvan Bourquin: The Impacts of Awareness Tools on Mutual Modelling in a Collaborative Video-Game. CRIWG 2003: 99-108

And I would call ‘mutual modeling acts‘ the interactions that aims at understanding what the partners is up to, will do, aims at or get from the situation.