Baking soda

sodium bicarbonate (white powder used in cooking, medicine, etc.)

Sodium bicarbonate is the chemical compound with the formula NaHCO3. Because it has long been known and is widely used, the salt has many other names including sodium hydrogencarbonate, sodium bicarb, baking soda, bread soda, cooking soda, bicarb soda or bicarbonate of soda. The word saleratus, from Latin sal æratus meaning "aerated salt", was widely used in the 19th century for both sodium bicarbonate and potassium bicarbonate. The term has now fallen out of common usage.
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Bak·ing soda n. A white crystalline compound, used as a gastric and systemic antacid, to alkalize urine, and for washes of body cavities. [more]Baking soda - Community and Resources

Noun
1. a white soluble compound (NaHCO3) used in effervescent drinks and in baking powders and as an antacid
(synonym) bicarbonate of soda, sodium hydrogen carbonate, sodium bicarbonate, saleratus
(hypernym) bicarbonate, hydrogen carbonate

A leavening agent, activated by interacting with something acid. Liquid ingredients like sour milk, sour cream, buttermilk, yogurt, molasses, and lemon juice help baking soda produce the gases which in turn make a batter rise. The batter should be baked as soon as possible after the liquid has interacted with the baking soda.