A CICS transaction is considered to be a unit of processing initiated by a single request that may affect one or more objects. This process is usually screen oriented, but background transactions are also supported.
One of the advantages of CICS is that applications written for this, can be written in a host of different programming languages, as they all use CICS language extensions to interact with the resources such as files, database connections, terminals, or to invoke functions such as web services. CICS manages the entire transaction such that if for any reason a part of the transaction fails all recoverable changes can be backed out.
Example of usage – “CICS Transaction Server (CICS TS) sits at the head of the CICS family and provides services that extend or replace the functions of the operating system.”