Simple Definition:

“Acidity” is a measure of how sour or sharp a substance can be. It tells us how much of a certain kind of chemical exists in the substance. Acids, which have high acidity, can be corrosive. Corrosive means that acids have the ability to cause damage or wear away certain materials, like metals or skin, when they come into contact with them. For example, lemon juice, which is acidic, has high acidity, making it taste sour.

Very Simple Definition:

“Acidity” is a measure of how sour a substance can be. It tells us how much of a certain kind of chemical exists in the substance. Some acids, which have high acidity, can be corrosive, meaning they can cause damage to things they touch. For example, lemon juice is acidic, which makes it taste sour.