Logical process in the R/3 System.
From the user's point of view, a transaction is a self-contained unit (e.g. generate a list of customers, change the address of a customer, book a flight reservation for a customer, execute a program).
In terms of dialog programming, a transaction is a complex object that consists of a module pool and screens, and is called with a transaction code.
After logon, there are 3 distinct levels in the R/3 System:
A transaction is a task performed at task level. To execute a transaction starting at main menu level, you either navigate through the menus by choosing the appropriate menu options, or you enter the appropriate 4-character transaction code in the command field and go directly to the task level.
Suppose you want to execute a transaction in the ABAP Workbench. To access the first screen of the task from the main menu level, choose Tools -> ABAP Workbench -> ABAP Editor , or enter the transaction code SE38 in the command field.
A business dealing which involves a payment card used to purchase goods or services and leads to crediting the merchant and collecting money from the cardholder or issuing bank.