Bleed
Bleed is the portion of a card design that extends past the cut line, so a small misalignment in the cutting machine doesn't leave a white edge along the border. Most print shops, including TheGameCrafter, want 0.125" (3.175 mm) of bleed on every side.
Why it matters
You hit bleed the first time you upload a card and the printer rejects it for "missing bleed." Backgrounds and full-bleed art need to extend into this margin, even though it gets trimmed off.
Example
A poker card is 2.5" × 3.5" trimmed. With bleed, the actual file you upload is 2.75" × 3.75" — the extra 0.125" on each side is the bleed zone.