This option lets you visualize trapping in the proof and set special options that can differ from the trapping options for imaging.
"Trapping" is a term that is widely used in the graphic arts industry. This term refers to the spreading and choking performed between two abutting colors. Trapping is used to avoid "flashes", in other words, unwanted white lines or color margins at color transitions that are the result of register errors in printing. The trapping option lets you add thin lines ("trap lines") to the margins of color transitions that cover the colors of other separations that may shine through or empty regions ("flash lines").
Trapping can take place on the basis of vector data (graphics) or pixel data (images). It is possible to trap graphic to graphic, graphic to image and image to image. Trapping within images is not supported.