This is the 7669th most frequent French word.
roche
Rock.
Here, 'roche' is used in its singular form to indicate a specific rock, a large piece of stone often found naturally.
La roche au bord de la rivière est couverte de mousse.
The rock at the riverbank is covered with moss.
In this sentence, 'roches' is plural and refers to volcanic rocks, indicating a category of stones formed from volcanic activity.
Les roches volcaniques contiennent de nombreux minéraux.
Volcanic rocks contain many minerals.
'Roche' is again singular, this time referring to a specific rare rock in the context of scientific study.