Printing from the SAP System 
Features
Using the SAP output system, you can output many types of documents on output devices such as printers or fax machines: purchase orders, invoices, delivery note, payroll documents, e-mails, report lists, and so on.
Process Flow
Unlike most other
programs, which forward print requests directly to the printer, the SAP System
temporarily stores the print data. If you want to print data in an SAP System
(online or in the background) and
choose a print function, such as 
, the SAP output system creates two types of
print requests:
...
1. a spool request, which temporarily stores the data to be printed in the system
2. an output request, which sends the data to the desired output device
If you want your document to be printed immediately on your printer without temporary storage, you must have made a setting in the print window for immediate output. In this case, the spool request and output request are generated immediately, and the data is printed.
If you want to temporarily store the data, do not choose print out immediately. You can display the temporarily stored print request (spool request) in the output controller and/or print it at a later time.
More Information
BC - SAP-Printing
Manual