The terms “bleed” and ”trim” might sound like overly complicated technical jargon but in reality, they’re extremely easy to understand.
It’s extremely important that you account for bleed and trim when designing for print, so here’s a simple explanation of each:
Bleed
Just as it’s possible for there to be small discrepancies in the trimming process which may eat into the trim area slightly, it’s also possible for those same discrepancies to go the other way (i.e. the actual trim line is slightly outside the trim area). Without a bleed area, you’d be left with random ugly white lines around your finished product if this happened. The bleed area is there as insurance, to prevent your design from looking ugly no matter what happens.
Bleed varies between book printing companies but it’s typically around 3mm in the China.
Trim
The outer edge of the trim serves as the cut line where the product will be trimmed when it comes out of the printer. In theory, anything outside of that trim line will be cut off and anything inside will remain. However, things aren’t always 100% accurate down to the millimetre, which is why you leave a trim area to account for any small discrepancies.
The idea behind the trim area is to ensure that no matter what happens, no important content is ever trimmed from the design by accident.
Safe Area
The safe area is the area in which all of your important information and design elements should reside. It’s called the safe area because no matter what happens, everything inside this area is 100% safe and will be included in the final printed product. No important part of your design (aside from the background) should extend outside of the safe area and into the trim area.
Trim varies between printing companies but it’s typically around 3mm in the China.