The term for extra inventory held to protect against demand or supply uncertainties is safety stock.
Safety stock is inventory kept above the expected requirement so an operation can continue when customer demand is higher than forecast, replenishment takes longer, or deliveries arrive short. It is a buffer against variability rather than stock intended to meet ordinary planned demand.
Companies set safety-stock levels using factors such as demand variability, lead-time variability, desired service level, and the cost of running out. More safety stock can reduce stockout risk, but it also ties up cash and increases storage, insurance, and obsolescence costs. The right amount is therefore a trade-off, not a universal number.
“Buffer stock” is often used as a near-synonym in supply-chain discussions, but safety stock is the standard inventory-management term in this question. Cycle stock is the inventory consumed between routine replenishments, while dead stock is inventory unlikely to sell or be used.