ERP stands for enterprise resource planning. That expansion explains almost nothing, and the term gets used loosely alongside MRP and MES until none of them is clear. This is a plain explanation of what ERP means in a manufacturing context, and how the related terms fit together, written for people who want the concept rather than the jargon.
The literal term
"Enterprise resource planning" was coined decades ago to describe software that plans and manages the resources of an entire business. The phrase is dated and abstract, and it is fair to mostly set it aside. What matters is what the software does, not what the three letters unpack to. Nobody chooses an ERP because of the acronym.
What ERP means in practice
In practical terms, an ERP is one connected system that runs the core operations of a business: sales, inventory, purchasing, production, and finance, as a single model rather than as separate tools that pass files to each other.
The defining quality is that the parts are connected. An action in one area flows correctly to the others: a sale becomes a demand, a demand becomes a production and purchasing plan, production reports back to cost and inventory, and all of it reaches the accounts without re-keying. When people say a business "runs on ERP", they mean it runs on one system instead of a patchwork, so that everyone is working from the same numbers.
The manufacturing-specific parts
A general ERP handles sales, inventory, and finance for many kinds of business: a distributor, a retailer, a services firm. A manufacturing ERP adds the parts specific to making things.
That means the bill of materials, the structured definition of what a product is made of; work orders and routings, which describe how a product is produced and on which work centers; production planning; shop-floor tracking of what actually happened; and the costing of a product that is assembled from components and labour rather than simply bought and resold. When the term ERP is used in a manufacturing setting, it is this fuller meaning that is intended, and a system without those parts is not really a manufacturing ERP.
ERP vs MRP
MRP stands for material requirements planning. It is older and narrower than ERP. MRP answers one specific question: given demand, current stock, and lead times, what should we make and what should we buy, and when?
MRP came first, historically, and modern manufacturing ERP includes MRP as one of its functions. So the relationship is simple: MRP is a capability, and ERP is the whole connected system that contains it, alongside sales, purchasing, inventory, costing, and finance. If someone offers you "an MRP", they are offering a planning tool, not a full business system.
ERP vs MES
MES stands for manufacturing execution system. Where ERP plans and manages the business, MES focuses tightly on the shop floor in real time, tracking exactly what each machine and operator is doing, moment to moment, often connected directly to equipment.
In smaller and mid-sized manufacturers, the shop-floor tracking built into a manufacturing ERP covers what is needed. Larger or highly automated plants sometimes run a dedicated MES alongside the ERP, with the MES handling real-time execution and the ERP handling planning and management. ERP is the planning and management layer; MES is the real-time execution layer; the two are complementary, not competing.
The short version
ERP is the one connected system a business runs on. A manufacturing ERP is that system with the production-specific parts, BOMs, work orders, routings, included. MRP is the planning capability inside it. MES is a separate, shop-floor-focused layer that larger plants sometimes add on top. If you remember only one thing, remember that ERP is about everything being connected, so the business works from one set of numbers instead of several that disagree.