What is bleed?

Bleed means your work must go beyond the sheet after trimming.
In the picture, bleed is between the black line (cutline) and the red line.
Why does your art file need to be larger? Because your work needs to be trimmed after printing to get the right size.
For example, a standard business card is 9cm x 5.5cm. An art file that has exactly the same size will encounter issues when cutting because we cut a stack of card at the same time. This means some cards may move, creating white edges around your work. It will look untidy. To prevent this from happening, it is important that you include at least 3mm bleed when designing your artwork. Your file should be 9.6cm x 6.1cm to get perfect 9cm x 5.5cm cards.