Degrees Brix (symbol °Bx) is a measurement of the dissolved sugar-to-water mass ratio of a liquid.  For example, a 26 °Bx solution is 26% (s/w), with 26 grams of sugar per 100 grams of solution.  It is used in winemaking to determine the sugar content of the wine grapes (generally measured with a refractometer), as well as to estimate the final percentage of alcohol of the finished wine (measured with a hydrometer).  As wine must ferments, the sugars are converted to alcohol, and the brix reading drops.  A wine fermentation is considered “dry” when brix are at approximately 0 °Bx.