Sodium bicarbonate is baking soda, bicarb or bicarbonate of soda. It is a chemical compound, sodium hydrogen carbonate, with the formula NaHCO3. The elements within it are sodium, hydrogen, carbon, oxygen. It is a white crystalline powder.
It is an antacid: it was in the past to relieve acid indigestion. This is a digestive problem where there is too much acid in the stomach. When there is too much acid, it causes heartburn, an uncomfortable feeling in the stomach. It reacts with acids to produce carbon dioxide gas. It also reacts with bases to reduce their harmful effects.
Baking soda is rarely found in the earth. It can be manufactured artificially, though.