To “proof” means to produce a proof or have a proof produced. “I still need to proof the brochure” is the typical phrase for the word “to proof”.
Proofing thus means to have a colour and legally binding proof produced according to the current ISO 12647-7 standard. The current valid revision of this standard is ISO 12647-7:2016, which regulates the central parameters for “proofing” such as target tolerances and specifications for producing the proof, the job tickets and the test report.
Only when an UGRA/Fogra or, for the American proofing standards, an IDEAlliance media wedge is printed does the proof become a proof, i.e. the proofing process differs from the printing process. This media wedge does not have to be measured, but it is of course helpful for the printing company if it does not have to measure first but can see at first glance that the proof has been produced in colour and legally binding according to the current standard.