Brown sugar is now the name for the cassonade. These fine crystals of sugar mainly from sugar cane juice.
(There are also brown sugar from sugar beets, called “brown sugar” and traditionally consumed in northern France and Belgium.)
Brown sugar is not refined yet imbued with a thin layer of molasses. Molasses, it is the brown sugar syrup obtained in the final stages of crystallization.
What is brown sugar.
Note that these days the so-called brown sugar is almost always white sugar, more refined, with the addition of molasses and sometimes an artificial flavor and color.
Adding more or less burnt sugar, which acts as dye for brown sugar or dark. The real brown sugar and real sugar, which does not come from the white sugar processing, have a more subtle taste.
Read more here about brown sugar.