In job interviews sometimes a question is asked, about how many databases were in your oganization? ERP uses a single comprehensive database containing modules for major back-office functions within a business. Most of the major ERP systems came out of a manufacturing or operations driven background, so they have modules that covers these business functions very well. ERP System may includes:
Manufacturing – Engineering, Capacity, Workflow management, quality control, bills of material, manufacturing processes.
Financials – Accounts Payable, Accounts receivable, fixed assets, General Ledger, Cash Management.

Human Resource: Benefits, training, payroll, time and attendance, etc

Supply Chain Management: Inventory< Supply chain planning, supplie scheduling, claim processing, order entry, purchasing

Projects: Billing, Costing, Activity management, time and expense etc.
Customer relationship management: Sales, Marketing, Service, Commissions, customer contact, Call center support etc.

Data Warehouse: Usually this the module that can be accessed by an organization’s customers, supplies and employees.
 

A caution about ERP systems – Companies need to be willing to change their mentality around how they do things to fit into how the system requires it. If companies try to tailor an ERP system with too much customization it will fail.

Source: Certified Management Accountants Canada – 2009 IT Topic