Xocoatl is the raw, unsweetened form of chocolate. A word from the Nahuatl language, xocoatl derives from xoco, bitter, and atl, water, and is the source of the word chocolate itself. Xocoatl is taken immediately from the cacao bean before processing, and although used to make chocolate later on it has an extremely bitter taste. In making chocolate, sugar is added and the bitter taste is replaced by sweetness.
When Spanish conquistadors first visited the Aztecs they were served cups of hot, unsweetened chocolate. When the Spanish found the word "Xocoatl" difficult to pronounce, they began calling the drink "chocolat".
-Taken from Wikipedia