ERP
ERP usually coordinates company-wide resources such as accounting, purchasing, inventory and business processes.
OMS
An order management system focuses on the order lifecycle across channels and fulfillment.
WMS
A warehouse management system focuses on physical warehouse execution.
Why commerce blurs the lines
Modern eCommerce needs these workflows to remain connected around the same order context.
Map the system boundaries before buying
List where product data, orders, inventory, warehouse execution, payments and reporting will live. The key question is not the product label but how those systems exchange operational context.
Avoid duplicate sources of truth
If two systems can both edit the same stock or order state, governance becomes critical. Define which application owns each record and which applications consume it.
Every event should remain connected to the product, contact or transaction that created it. That is what lets ERP explain a number instead of only displaying it.