Overprinting means that one colour gets printed directly on top of another colour.
Sometimes in printing, it makes sense to allow the top objects in a piece to print directly on top of other fully printed objects.
Effectively separating the colour from the rest of the print, it is primarily used for 'Spot Colours' (Pantones) or for specialist finishing such as foiling or die-cutting.
If we print (as normal) with overprint off, the colours underneath are 'knocked out', which delivers a vibrant pure colour. You are basically printing the colour on white. The disadvantage of this is that a small white line can be visible if the origination is slightly misaligned.
When overprinting, the ink or foil is printed directly on top of the base colours.
