A mixture of alcohol and water containing (in the UK) 57.1 per cent alcohol by volume or (in the US) 50 per cent alcohol by volume, used as a standard of strength of distilled alcoholic spirits.
标准浓度酒（酒精含量英制为57.1%，美制为50%）
Definition of proof spirit in US English:
proof spirit
nounpro͞of ˈspirit
A mixture of alcohol and water containing (in the US) 50 percent alcohol by volume, or (in the UK) 57.1 percent alcohol by volume, used as a standard of strength of distilled alcoholic liquor.