A paper fold is a printing error caused by creasing of the paper. When the sheet is later flattened, the affected area may appear as a characteristic unprinted white strip across the stamp design.

The crease usually develops because the paper is not fed correctly through the press. While the sheet remains folded, the printed image may appear continuous across the raised surface. Once the paper is flattened, however, the previously folded section opens out and reveals an unprinted white band.

Paper folds can occur with many printing processes and paper types. Visually striking examples are popular with collectors, and some catalogues list them separately. In general, the wider and more conspicuous the unprinted strip, the more significant the variety.