Analog audio recordings have two limits, a quiet noise floor where signals become inaudible and a loud upper ceiling where a system may create gross distortion and cause clipping. The space between the two extremes is the dynamic range.
Until the very last stage of mixing and mastering, an audio engineer attempts to keep levels at a “sweet spot” where there is plenty of margin for the range of the recording. The upper capacity of the system above the sweet spot is the headroom, and making the best use of it allows the reproduction of the audio to capture every nuance of the sound.
Though ideally largely unused, headroom refers to the space or buffer zone that accommodates the unexpected in order to create natural sounding highs, lows, and volume. National Audio’s Ferromaster C456™ tape provides greater headroom than other ferric tapes.