What’s that in English?
Basically all the measurments in the metric system are now based on measurable physical properties. For example, the meter is based on the wavelength of light emitted from the atom Krypton. The sole exception is the kilogram which as the article mentions is based on an actual block of material stored in France. There used to be an actual “mother of all” meter sticks in France. The problem with the kg block is it changes over time so the kg is not a constant measure. The idea is to find some physical property that can be defined as a kg.