Trapping is a crucial operation in the prepress stage where two or more adjacent color areas sharing a common border are intelligently overlapped using a very thin stroke or bleed. The primary goal of trapping is to prevent the substrate's white material from becoming visible, or creating a slight gap along the color boundaries, which might occur due to slight material movement or minor, tiny errors in the printing press register. Trapping automatically expands one color slightly underneath or over the adjacent color, establishing a small safety zone for overlap. This region is extremely small and barely noticeable under normal viewing conditions, but it effectively hides the print registration error.

Trapping necessity intensifies significantly in printing processes like flexography due to the flexibility of the plates and the extensibility of the substrates, which drastically increase the potential for registration errors. Therefore, accurate trapping values must be calculated based on the specific press and material. Always prioritize spreading lighter colors under darker ones to maintain visual integrity and ensure clean color boundaries.