Have you googled? That is what I would do if I were to try to answer this. (But I am going to make a cold black and white bean sald w. lime coriander vinaigrette for 20 people, instead.)
“1. A process used in Halftone Photography that entails the temporary removal of the Screen during exposure. This increases the Highlight Contrast and diminishes the dots in the whites.
2. In halftones, removing the Screen for a short time to increase Highlight Contrast and drop out the dots in whites.”