A 1-per-page check is a single 8.5 x 11 inch sheet with one check on it, typically paired with one or two tear-off stubs for recording payment details — this is the standard "voucher check" format most businesses use.
Why it's the most common business format
The stub gives you a paper record of what the check was for without needing to look it up elsewhere, which matters for manual bookkeeping or when handing a physical copy to someone for their records. It's also simpler to align and proof than a multi-check sheet, since there's only one layout to get right per page.
The check itself can be positioned at the top, middle, or bottom of the page, depending on the stock — see our guide on top, middle, and bottom check layouts for how to tell which you have.