Dot gain
Dotgain or Tonal Value Increase is the difference between the halftone values in the original and the halftone values in print. This difference is caused by printing technology.
Lexicon
Dot proof
In the case of a dot proof, the halftone screening of the final print is simulated in the proof. This screening shows possible moiré or other disturbing effects, that by dot proofing can be seen in advance on the proof.