What does the term "proof" of an alcoholic beverage refer to?

The term "proof" of an alcoholic beverage is defined as a numerical measure of the alcohol content, specifically corresponding to twice the percentage of ethanol present in the beverage. For instance, if a drink has an alcohol content of 40% by volume, it would be labeled as 80 proof. This metric is primarily used in the United States and serves as a way to indicate the strength of an alcoholic drink to consumers.

Understanding this concept is crucial for recognizing how alcohol content is communicated and regulated, as well as for law enforcement and legal purposes, particularly in DUI and standardized field sobriety testing contexts.