The coordinates representing the "centroid" of the mass for that specific story. This is used by ETABS to calculate accidental eccentricity and torsional effects.
If you'd like to dive deeper into your specific project, tell me: building code you are following (e.g., ASCE 7-22, Eurocode 8). If you need help resolving irregularities (like torsional imbalance). How to export this data for manual base shear calculations. etabs mass summary by story
: The mass moments of inertia about the X, Y, and Z axes. RZ (rotational mass) is particularly vital for evaluating the torsional response of the building. The coordinates representing the "centroid" of the mass