During weather-based heat waves or cold snaps, a completely sealed house with all windows/doors shut (but using no HVAC, heating-ventilation-AC) will take "a while" to cool down or heat up. If the heat wave or cold snap is quick (e.g., 24 hrs), a resident inside the house will experience almost no change in temperature. On the other hand, if the wave or snap is long, after it's over, it'll take the sealed house some time to equalize with the normal outdoor temp. I'm not talking about air flow here; rather, it's the "capacity" for objects in the house (furniture, etc) to "hold" heat/cold. In physics (thermodynamics, etc.) what is this "holding capacity" called? It's not latent heat, as that requires state change. I've heard some refer to it as thermal ballast -- a term that is not formally described in any textbook.