Science has proof without any certainty. Creationists have certainty without any proof
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.