What is the term used to measure the strength of alcohol?

The term "Proof" is used to measure the strength of alcohol. It is a standard that quantifies the amount of alcohol in a beverage, expressed in a way that relates to its alcohol by volume (ABV). In the United States, proof is defined as twice the percentage of ABV. For example, if a beverage has an ABV of 40%, it would be considered 80 proof. This measurement provides a clear indication of the alcohol content, which is important for consumers and those in the alcohol service industry to understand the potency of various alcoholic beverages.

While "Percentage" does indicate the ABV directly, "Proof" is the more specific term traditionally used to represent the strength of alcohol in a standard format recognized widely in regulations and by consumers. "Grade" and "Volume," while relevant in other contexts, do not specifically convey the strength of alcohol in the same way that proof does.