Learning
A SKU is the unique code a store uses to identify one specific product variant, so it can be tracked, sold, and restocked without being confused with anything else.
A SKU (Stock Keeping Unit) is just a code. Its whole job is to let one specific variant, say, a red t-shirt in size medium, be told apart from every other variant in your store.
It sounds simple, and mostly it is, right up until it isn't.
Everything downstream of a sale depends on the SKU being right. Fulfilment, reporting, reordering, all of it assumes each variant has one clear, unique code.
When a SKU is missing, or the same SKU accidentally ends up on two different variants, that assumption breaks quietly. Nothing crashes. Reports just start being subtly wrong, and nobody notices until stock doesn't add up.
Ghost Stock checks for both of these specifically: variants with no SKU set at all, and SKUs that have been reused across more than one variant. Neither is treated as an emergency. Sometimes a missing SKU is genuinely intentional. But it's always worth knowing about.