Unit of measure
The unit a quantity is counted in — an each, a box, a case, a pallet, a roll, a metre.
Why it matters operationally
Adding two hundred to fifteen gives you the wrong answer if one of them is boxes. This is the single most common way a materials number goes silently wrong, because both figures look plausible and nothing in a spreadsheet objects. It also decides freight: pallets fill a truck, eaches fill a shelf.
How Roadmap handles it
Every catalog item carries its unit and its case pack, and totals are only ever added within a single unit. A department asking in boxes and a department asking in eaches are reconciled rather than summed.