My guess is the first thing that comes to mind immediately you hear the term, “transaction” is money and maybe followed by exchanging goods and services.
If my guess is right, then the smile on my face now is for you 
Transaction processing system (TPS) is an operational level computerized system designed to process and record routine transactions accurately. TPS supports, monitors and records business processes like accounting and financial transactions. This system is mainly operated by front line staff in an organization and decisions made here are highly structured.
Examples of Transaction processing systems in organizations are;
- Payroll systems
- Billing systems
- Payment and Funds transfer systems
- Production and Purchasing systems
- Stock control systems
- Order processing systems
- Reservation system
Roles of Transaction processing system
- Transaction processing system produce information for the other systems in an organisation
- TPS is used by supervisory and operational personnel
- The system sources information both internally and externally
Below is a table showing the Components of Transaction processing system;
The phases of a typical Transaction processing system is illustrated below;
The major characteristics of TPS are reliability, controlled processing, inflexibility and rapid response.
So yes I know what you are thinking, “your guess was not entirely wrong afterall”. 
Amin, M. B., Alauddin, M., & Azad, M. M. (2012). Business Transaction Processing System. International Journal of Computer Information System, 4.
Katavcic, M. (2001). Transaction Processing System. Information Process & Technology.
Mahajan, R. (n.d.). Role of Transaction Processing System.
Rahmatian, S. (2003). Encyclopedia of Information System. California: Elsevier Science.
mscisbolouereifidi 