This is the 7096th most frequent French word.
mers
Seas.
In this sentence, 'mers' refers to large bodies of saltwater, typically larger than lakes but smaller than oceans. It is used in the plural form to indicate multiple such areas.
Les mers sont agitées aujourd'hui.
The seas are rough today.
Here, 'mers' is used metaphorically to indicate various sea regions or maritime expanses that the subject explores.
Elle parcourt les mers à la recherche d'aventure.
She travels the seas seeking adventure.
In this context, 'mers' refers to the aggregate of seas when discussed as part of Earth's geography.