This is the 10752nd most frequent French word.
nappe
"Tablecloth" or "layer."
Here, 'nappe' refers to a tablecloth, which is a common usage of the word in French.
J'ai mis une belle nappe sur la table pour le dîner.
I placed a beautiful tablecloth on the table for dinner.
In this context, 'nappe' refers to an underground layer or sheet, like the water table.
La nappe phréatique sous cette région est très profonde.
The groundwater layer under this region is very deep.
Here, 'nappe' is used figuratively to describe a layer or blanket of fog.