olemus
alkohoolsete jookide etanoolisisalduse mõõtühik
ingliskeelsetes maades:
- USAs = kahekordne mahuprotsent
- UKs, kuni 1980 = 1,75-kordne mahuprotsent

Wiktionary:
11. (US) a measure of the alcohol content of liquor; originally, in Britain, 100 proof was defined as 57.1% by volume (no longer used). In the US, 100 proof means that the alcohol content is 50% of the total volume of the liquid; thus, absolute alcohol would be 200 proof

ülevaateid
https://en.wikipedia.org/wiki/Alcohol_proof