Bleed
CreativeExtra image area extended past the final trim edge so that if the cut lands slightly off, no white slivers show along the border. Standard print bleed is about 3 mm (1/8 in) on each side. Screen ads don't need it; print and large-format do.
Example
A flyer with a full-bleed background is built at 216×303 mm and trimmed down to A4 (210×297 mm).