The Glossary for MRO Spare Parts Inventory Management and Optimization

A method to group items by importance so you focus control where it matters most. A class gets the tightest controls, C class gets simpler rules. Combine ABC with asset criticality so low-cost but high-consequence items are not overlooked

An asset or part that drives disproportionate downtime, cost or safety risk. Bad-actor reviews often trigger stocking policy changes, design fixes or supplier actions

The structured list that links an asset or assembly to the parts required to maintain or build it. Accurate BOMs enable kitting, planning and optimization

Stock held at your site but owned by the supplier until issue or consumption. Useful to improve availability and reduce working capital for selected items

A structured method to rank assets or parts by consequence of failure. Results guide service targets, stocking policies and spare strategies

A perpetual inventory accuracy method where defined subsets of items are counted during normal operations. Often prioritized by ABC class or criticality

Two or more item masters that represent the same part. Duplicates hide true demand, fragment stock and create avoidable shortages. Eliminating duplicates is a fast way to recover cash and improve service

Buying outside normal lead times to address an urgent need. Frequent emergencies point to gaps in policy, forecasting or master data

A system that plans and controls work, assets and materials across the asset lifecycle. EAMs often include or integrate a storeroom module to execute policies

The demand pattern typical of many spares, with many zero-usage periods and irregular spikes. Intermittent demand requires policy and forecasting methods that can handle sporadic consumption

A measure used to track performance against goals such as availability, fill rate, inventory turns or working capital

Preparing all parts and materials required for a planned job so technicians can start work without delay. Effective kitting depends on accurate BOMs and reliable picking

Elapsed time from reorder to ready-to-issue, including approval, supplier processing, manufacturing or picking, transit, receiving and put-away. Lead time drives safety stock and reorder points

The activities and supplies that keep facilities and production assets operating. In this glossary, MRO refers to the materials that support maintenance and repair work, including spare parts, consumables, hand tools, and standard replacement parts used for planned and corrective maintenance. It does not include items such as PPE, chemicals, or production raw materials.

The item master, attributes and references that define each spare part. Quality master data links parts to assets and documents such as BOMs and prevents duplicates

A simple control method where a minimum (or reorder) level triggers replenishment and orders target a defined maximum. The minimum level can include or be set above the safety stock, which protects availability for critical or unplanned-demand spares. This approach is widely used for large catalogs and is easy to execute in most systems.

Stock that is no longer required because assets are retired, designs change, or items are no longer serviced or produced by the supplier. Tie BOMs and change control to stocking policy to avoid building or retaining obsolete inventory.

Deliberate placement of spares close to where work happens, for example a satellite store by a line or a secure cabinet at a remote pumping station. Speeds response time but still needs governance and visibility

The on-hand level that triggers a replenishment order. ROP is typically calculated as expected lead-time demand plus safety stock

A structured approach to define maintenance tasks based on how an asset fails and the consequence of that failure. RCM outputs feed stocking and kitting decisions

Extra stock held to protect against uncertainty in demand and lead time. It is often comparable to the minimum stock level but serves a distinct purpose: safety stock specifically protects availability for critical spares and unplanned work, not for materials used in planned work orders. Safety stock is sized to meet a chosen service level for each item or policy group

A design target that sets the probability of not stocking out during a replenishment cycle. Different from fill rate, which measures immediate availability

Any replaceable or interchangeable component or subassembly defined to restore function during maintenance or repair. A spare part may be physically stocked or listed in a BOM for interchangeability and standardization purposes. In practice, MRO inventory includes these spare parts as well as consumables and standard replacement materials used in maintenance work

A situation where demand cannot be met from available stock. Stockouts expose availability risk and often lead to emergency orders or cannibalization

An arrangement where a supplier monitors and replenishes inventory at your site to agreed targets and policies for selected items