the.com/soda bread

means A quick bread leavened with baking soda instead of yeast, traditionally made with flour, salt, and buttermilk, whose acid reacts with the soda to make it rise.

from The 'soda' is sodium bicarbonate — baking soda — which, when it meets the lactic acid in buttermilk, fizzes up carbon dioxide and lifts the dough without any waiting around for yeast to do its slow work. The technique spread widely in Ireland in the 1800s, where soft wheat (poor for yeasted bread) and the easy availability of bicarbonate of soda made it a practical staple; it's why soda bread is so strongly associated with Irish baking, though similar soda-leavened breads arose elsewhere too. The traditional cross cut into the top is often explained as a way to let the fairies out, but more plausibly it just helps the thick dough bake through evenly.