Trapping: A slight overlapping that prevents gaps from appearing along the edges of graphic elements in film separations because of misalignments of plates in the press.
Even thought the above definition of trapping may sound scary, the truth could not be more further away. However, to understand trapping, a minimal knowledge of commercial printing is required (in specific knock-offs.) In commercial printing, all colors are made up of the four primary colors: Cyan, Magenta, Yellow and Black (CMYK). Thus, the wide gamut of colors is obtained by mixing the primary colors. For example, green is made up by mixing Cyan with Yellow as shown below.
 
Now, imagine you wanted the yellow to actually overlap the blue and not overprint (visible mix of colors.) Then the films would look something like this (this is not100% accurate but shown like this for simplicity’s sake):
 
Notice that the Cyan is actually “knocked off” where the colors overlap.
As simple as it looks, the very essence of this procedure makes way for the most overlooked pitfall of most DTP operators. The flaw is visualized in white fuzzy lines around small graphic objects such as text (normally due to the “montage” operators’ misaligning separation films slightly). Trapping a graphic object is simply bleeding (expanding the edges) slightly as a safe guard. The visual below shows this clearly:
 
How to trap in QuarkXPress?
Trapping could not be easier in QuarkXPress, simply:
Select the desired graphic object to be trapped (highlight it).
Choose Show Trap Information (View Menu) option-F12
Fill in the desired amount of trapping
 
I hope everyone had a Happy Turkey trapping day! : )
