Kshar (Alkali) is a substance that, when mixed with water, raises the pH of the water to more than 7.0. According to Brunsted and Lowry, a base is a substance that donates OH- too acidic substances.

Bases are actually substances that combine with acids to form salts and water. For example, zinc oxide combines with sulfuric acid to form zinc sulfate and water. Caustic soda combines with sulfuric acid to form sodium sulfate and water. Oxides of metals are generally bases. But there are exceptions to this as well.