Terroire = The “spirit” of the soil in which the grapes are grown.
"Terroir" is the characteristic taste & flavor imparted to a wine by the environment in which it's produced." – dictionary definition.
Terroir includes environmental variables – mostly soil chemistry, but also the amount of daily & seasonal sunshine, and statistical rainfall + humidity.
Terroir is a nickname for the properties that make certain vineyards' locations suitable for different wine-grape varietals.
A specific terroir is a "signature" of a region known for producing high quality grapes, like the Hewitt & To Kalon vineyards in the [small] Rutherford "bench" of Napa Valley.
Terroir can be significantly different between vineyards located near each other – different soils & microclimates [fog].
Grapes from vineyards in cool, coastal climates are better suited for white & sparkling wines, like Chardonnay & Pinot Noir in the Carneros region.
"I have tasted many French wines. They lack the essence of California sunshine." – quote from a knowledgeable Napa Vally winemaker, summarizing the difference between hot, dry NV summers vs. Bordeaux vineyards often soaked by summer rain.
I agree.