SAP R/3 is structured around modules. These modules are business functions within a company.
Financial Modules
FI – Financial Accounting
CO – Controlling (Management Accounting)
IM – Investment Management
PS – Project Systems
FSCM – Financial Supply Chain Management (Old modules CFM and TR are part of FSCM now)
Logistics Modules
SD – Sales and Distribution
MM – Material Management
QM – Quality Maintenance
PM – Plant Maintenance
PP – Production Planning
Human Resources Modules
PA – Personnel Management
PT – Personnel Time Management
PY – Payroll
These are part of ECC (ERP central Component) in MYSAP releases.