A parameteris an object passed to a procedure by the procedure invocation statement. Note that the term “procedure” is used here, as it is throughout this guide, to refer to complete programs as well as to subroutines within a program. Most programming languages can pass parameters to procedures. Parameters can be of many types, and in each language, most or all of the types of available variables can be passed as parameters.

Each parameter has two aspects: an actual parameter and a formal parameter. The actual parameter is the parameter specified in the procedure invocation statement. The formal parameter is the parameter as it is declared in the procedure that is being invoked.

Parameters that are used in a process initiation statement provide an avenue of communication between the initiating process and the new process. Such parameters are referred to hereafter as tasking parameters.

Parameters that are used in a library procedure invocation statement provide another type of interprocess communication. Such parameters are hereafter referred to as library parameters.

The Determining the Scope of Parameters and Parameter Passing Modes subsections of this section provide information that is relevant to both tasking parameters and library parameters. The remainder of this section addresses only tasking parameters. For further information about library parameters, refer to Using Libraries.