Terroir has nothing to do with terror, horror movies, or upcoming Halloween. Instead, terroir is a French word derived from Latin "terra" and French "terre" meaning the earth.
Most often it's used to refer to the natural conditions of soil, sun, weather, climate, et al, that produce specific flavors in food and drink. In other words, it's the agricultural version of "we are what we eat." We all more or less know this even if we don't think about it much, but in wine cultivation, terroir is an important concept. I might add that I am no wine specialist and my house wine is box pinot grigio, which is a perfectly good table wine.
But the concept of terroir is interesting. I started thinking about it when I was writing my most recent book, Once a Soldier. My fictional San Gabriel is a small kingdom between Portugal and Spain and wine is its most significant product. and the only one that has the potential to bring in revenue through exports.