In printing terms, a bleed is extra colour that extends beyond the edge of the finished sticker edge.
Why is a bleed necessary on my sticker?
There is always a small amount of movement within the machine while cutting stickers. Although we try to achieve a perfect cut, we like to give up to 1mm of wiggle room. (And when we say wiggle, it is because the machine literally wiggles!)
By having an extra bit of colour around the edge, there is room for error, without suffering consequences. Without the bleed, we could end up with a white line on one side of the sticker.
Typically we only require a 3mm bleed.
In the picture examples here, the pink line indicates the cut line. This is where the stickers will cut out. Note the white outline on the sticker "without bleed" - this is what we are trying to prevent!