MES: An MES (manufacturing execution system) is software that tracks and controls work on the shop floor in real time, recording which job runs on which machine, by whom, and with what result.
Where an ERP knows that an order exists and when it is due, an MES knows what is happening to it right now. It dispatches jobs to machines and operators, records start and finish times, collects machine data, tracks scrap and rework, and keeps the traceability record that regulated industries need.
Example: a print farm’s MES shows that printer 7 started a batch of 24 parts at 08:10, paused for a filament change at 11:30 and finished at 14:05, with two parts scrapped. That record feeds the quality log and tells the scheduler when printer 7 is free again.
That same data is valuable for pricing. Actual run times from the MES are what you need to check your quoting estimates, a process called calibration. Machine states from the MES are also the raw material for measuring OEE.
The common confusion is treating MES and ERP as one product. Some vendors sell both, and the boundary varies, but the roles differ: ERP plans and accounts; MES executes and records. Many small shops do not need a formal MES at all, and a whiteboard or a printer-farm dashboard does the job.
Read ERP, MES and quoting for where each one starts and stops.
Go deeper: Quoting, ERP and MES: what each system should own and how they connect