CICS® 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, by request, at the same time as many other users are submitting requests to run the same applications, using the same files and programs.

CICS manages the sharing of resources, the integrity of data and prioritization of 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®). We could say that CICS acts like, and performs many of the same functions as the z/OS operating system.

A CICS application is a collection of related programs that together perform a business operation, such as processing a travel request or preparing a company payroll. CICS applications execute under CICS control, using CICS services and interfaces to access programs and files.

CICS applications are traditionally run by submitting a transaction request. Execution of the transaction consists of running one or more application programs that implement the required function. In CICS documentation you may find CICS application programs sometimes simply called "programs," and sometimes the term "transaction" is used to imply the processing done by the application programs.

CICS applications can also take the form of Enterprise Java™ Beans. You can find out more about this form of programming in the section on Java applications in CICS in the CICS Information Center.