ERP: An ERP (enterprise resource planning) system is business software that keeps a company's orders, stock, purchasing, production records and accounts in one shared database.
An ERP system is the record of the business. In a manufacturing company it typically holds customers and suppliers, sales orders, purchase orders, stock levels, bills of materials, routings, invoices and the general ledger. Work moves through it: an order is entered, materials are reserved, a job is released, the parts ship and the invoice goes out.
What an ERP usually does not do well is price a part nobody has made before. ERP quoting modules work from existing items, routings and price lists. For a new custom part, someone still has to estimate the machine time, often in a spreadsheet, and type it in.
Example: a job shop receives a STEP file for a new bracket. The estimator works out 25 minutes of milling and enters a new item and routing in the ERP so the job can be scheduled and invoiced. A quoting tool can produce that estimate from the file; the ERP then carries the order from there.
ERP is often confused with MES. The ERP plans and records at the business level (what was ordered, what it cost, what was invoiced); the MES tracks what is happening on the shop floor, minute by minute. Many smaller shops run without either and use spreadsheets.
For how ERP, MES and quoting fit together, read ERP, MES and quoting.
Go deeper: Quoting, ERP and MES: what each system should own and how they connect