There will be different types of events in ABAP.
Events in Dialog Program
PBO - Process Before Output
PAI - Process After Input
POH - Process on Help
POV - Process on Value Request.
Events in Classical Report
INITIALIZATION
AT SELECTION-SCREEN OUTPUT
AT SELECTION-SCREEN
START-OF–SELECTION.
TOP OF PAGE
END OF PAGE
END-OF-SELECTION.

Control Break events related to Internal Tables
AT NEW FIELD
AT END OF FIELD
AT FIRST
AT LAST
Events in Interactive Report [...]