If you have proof of something then you have evidence that is factual and that can not be defended against. Proof quotes can be found online in a number of locations, and the proof of alcohol refers to the actual alcohol content that a drink has. A proof can also be an item that is created for approval before printing or publication starts. If you have a photograph of your spouse in a compromising position with someone else then you have concrete proof of infidelity. Some alcohol may be as low as 30 proof while others can be far higher. Moonshine is usually a very high proof and it only takes a little for someone to get drunk. If you have someone proof your work then they will go over it and detect any mistakes that need to be corrected.