ABAP memory is the temporary memory storage used by ABAP programs and objects that are using the same internal session - or same memory area - for all activities. Compared to SAP memory, which is considered a global memory, ABAP memory is a local memory. ABAP memory is independent of the ABAP programs or objects that generate it, thus making it possible to transmit values across different objects or programs irrespective of their characteristics. This is particularly useful for programs that are live in the same session.
Techopedia explains ABAP Memory
ABAP programs and objects mainly use two types of memory: ABAP memory and SAP memory. ABAP memory is pretty limited in scope compared to SAP memory, and can be accessed by one main internal session, while SAP memory is accessible to programs or objects outside the main session. ABAP memory is one of the important tools available for programmers for transmitting values across programs. It helps in minimizing the database usage and also helps in maximizing the speed and efficiency of the applications.
The values transmitted through ABAP memory are not stored in any SAP table. To access the ABAP memory, statements using the keywords "Export to Memory" and "Import from Memory" are used. "Export to Memory" is used to read data from ABAP memory, whereas "Import from Memory" is used to write data from ABAP memory.