Solutions with a pH below 7 are considered acidic, while those above 7 are basic or alkaline. The pH scale measures the acidity or alkalinity of a solution and ranges from 0 to 14. pH is important in many fields including medicine, biology, chemistry, agriculture, forestry, food science, and engineering. It plays a key role in processes like tooth decay prevention through basic toothpastes, plant and animal sensitivity, soil chemistry, digestive systems, and chemical defenses in nature.