Brut is the French word for raw (about material or data), crude (about oil) or uncut (about diamonds). In wines it is the term used to describe a dry wine (usually Champagne or sparkling wines).
That a wine is dry doesn’t necessarily mean that it is devoid of sugar. Brut simply means that the wine has the least residual sugar. Brut Natural or Brut Zero are terms used for wines without any residual sugar. A dry wine with more sugar is called sec or demi-sec. Make no mistake, though, we’re still talking about a dry wine.