Global Definitions 
Global definitions apply for the entire form. You can use any objects defined there in all nodes of the tree.
The following global definitions are possible:
Variables or constants whose types are stored in the ABAP Dictionary
Types as free ABAP coding, provided there is no type in the ABAP Dictionary
You can initialize the global data before you start processing the start page. Usage examples are: conversion of selected application data, optimizing form logic by previously reorganizing internal tables, and so on.
On the Form routines tab you enter routines that you want to use in the form via the program lines node. Within these form routines you cannot access any global data unless you explicitly pass them to the form routine interface.
To maintain global definitions use the node .