Difference Between User Exit and Customer Exit in SAP ABAP Enhancements.

The Enhancement Concept allows us to add our own functionality to SAP's standard applications. It allows to  create specific programs, screens and menus. There are two main types of enhancement, such as user exit and customer exit.

USER EXIT

• Implemented in the form of Sub routine.
• Accessibility to all data in case of perform.
• It is often considered to be a modification instead of enhancement.
• Looses changes in case of upgrades.
• Access key required