Mercalli intensity scale
The Mercalli intensity scale (or more precisely the Modified Mercalli intensity scale) is a scale to measure the intensity of earthquakes. Unlike with the Richter scale, the Mercalli scale does not take into account energy of an earthquake directly. Rather, they classify earthquakes by the effects they have (and the destruction they cause). When there is little damage, the scale describes how people felt the earthquake, or how many people felt it.
Very often, non-geologists use this scale, because it is easier for people to describe what damage an earthquake caused, than to do calculations to get a value on the Richter scale.
Values range from I - Instrumental to XII - Catastrophic.