Proof

Proof could mean: 
 An argument, including:
 Mathematical proof
 Proof theory, a branch of mathematical logic
 Logical argument
 Evidence (law), tested evidence or a legal proof
 Proof (alcohol), measure of an alcoholic beverage's strength
 Proofing (baking technique), how a yeast-leavened dough rises
 Proofreading
 Artist's proof, a single print taken during the printmaking process
 Proof coinage, a coin made as an example of a particular strike
 Proof test, for a firearm
 Galley proof, an early version of a publication
 Homeopathic proving, testing a substance's effect on the body

In entertainment:
 Proof (1991 movie), an Australian movie by Jocelyn Moorhouse
 Proof (play), a play by David Auburn
 Proof (2005 movie), a movie directed by John Madden, based on the play
 "Proof", a song by Paul Simon from his 1990 album The Rhythm of the Saints
 Proof (rapper) (1973-2006), American rapper, a member of the group D12