The gray frame is a bleed area of about 4mm, for cutting cards during the production process. If you have a photo that reaches the edge of the card, this "indentation" should be covered with your photo. This prevents the appearance of white print lines between the photo and the edge of the card since we cannot predict exactly where the cut will be in this 4 mm area (it is a mechanical process).

Be careful not to include text in this area as it is likely to be cut off.