Also called buffer stock, minimum stock
Safety stock is the extra quantity you keep in case things do not go to plan. Sales might jump before a festival, or a supplier might deliver three days late. Safety stock covers the gap so the shelf does not go empty.
Too little and you run out of your best sellers at the worst time. Too much and cash sits on the shelf. The right amount depends on how unpredictable the product's sales are and how reliable the supplier is. Fast sellers with unreliable suppliers need the most.
A shop normally sells 10 bottles of an oil a day, but on busy days it sells 16. Its supplier sometimes runs 2 days late. Keeping about 30 extra bottles covers a few busy days or a late truck. That 30 is added on top of the expected sales during the lead time to set the reorder point.