Information systems that collect, store, modify and retrieve records of transactions are transaction processing systems. A transaction is an event that generates or modifies data that is eventually stored in an information system. Transaction processing systems meet record keeping and event tracking needs. In addition, analysing data stored in transaction processing systems may meet the information needs of end user(s). This option focuses on the information process of storing/retrieving. Other information processes are important in transaction processing and these are also considered.
text taken from IPT Syllabus, section 9.4.1: Transaction Processing Systems introduction.
tl:dr - it's a database on a network!
The characteristics of a TPS include rapid processing, reliability, standardisation and control access. A TPS processes data in either real-time, which presentsÂ