Each balloon could be filled or designated with a color. The number of colors used in the picture is the number of plates needed to print the same art. Spot colored artwork requires a separate plate or sheet for each color used in the art. For example, if your art included the colors red, purple, yellow and black, the color separated art would be made up of four separate sheets. These sheets include printer's marks or crop marks in the corners which allow the printer to line up the colors and achieve a tight registration between them.
Trapping refers to the amount of overlap between colors.
It is imperative that the proper amount of trap is provided for the printer. The amount of trap required should be determined by the printer and may be dependent on the method of imprint.