If you want to know what CICS TS is all about... This is the publication to get!
In this IBM® Redbooks® publication, we discuss CICS®, which stands for Customer Information Control System. It is a general-purpose transaction processing subsystem for the z/OS® operating system. CICS provides services for running an application online where, users submit requests to run applications simultaneously.
CICS manages sharing resources, the integrity of data, and prioritizes execution with fast response. CICS authorizes users, allocates resources (real storage and cycles), and passes on database requests by the application to the appropriate database manager, such as DB2®.