Low-level formatting
Drawing the physical track-and-sector grid onto a blank disk — not creating a filesystem.
Low-level formatting writes sector headers, gaps and address marks and sets the sector interleave; it lays down the very grid a filesystem later keeps its books on top of. On old MFM drives the user did this themselves via the BIOS or DEBUG, often with a hand-picked interleave factor.
Modern IDE/SATA disks are low-level formatted at the factory with embedded servo information and cannot genuinely be redone by the user — the tools that promise it merely zero-fill the surface. Confusing it with high-level formatting (laying down FAT or NTFS) is a classic support call.