Q.1) What are SAP reports?
Ans: SAP Reports are event-driven programs using ABAP/4 programming langugage. These reports are used to fetch business-specific data from SAP standard databases under specified selection criteria, fetched data is processed to display result on output screen. User develop SAP report object on ABAP editor using the standard SAP transaction SE38.
Q.2)What are [...]

REUSE_ALV_EVENTS_GET: Returns table of possible events for a list type
=======================================================================
After preparing the fieldcatalog the next step is to build an event table for both user commands and system dependent events like top of page, end of page etc. and to print data at the top of the list, at the end of the [...]

There is no mandatory event in a report program. Events are actually used to organize the statements and control the flow of the program. If the program contains no explicitly defined event blocks, all the statements in the program form the entire event block START-OF-SELECTION. ABAP runtime environment automatically introduces a START-OF-SELECTION at the first [...]