What is the meaning of proof in cooking?

Definition 1:

Evidence, either material or otherwise, needed to substantiate a claim.

Definition 2:

A proof run of coins or money checks that the machines are running, minting, or printing correctly. A proof is a coin or banknote from that run. Proof can also mean a special minting of coins or printing of bills that uses higher-quality materials and methods to produce items intended for sale to collectors.

Definition 3:

A measure of alcohol in terms of 1/200ths. E.g.: an alcoholic beverage that is 40 proof is 20% alcohol.