Variables are useful for establishing two-way communication between modules.

The answer is reference variable. To simplify, reference variables are valuable for creating two-way communication among modules. A reference variable is a codenamed in which that is another name for a previously existing variable. When a reference is primed with a variable, either the variable designation or the reference name may be used to talk about to the variable. In addition, there are some applied alterations among pointers and references. A reference is a codenamed for another variable while a pointer embraces the memory address of a variable. The references are usually used as purpose parameters so that the accepted object is not the copy but the object aforementioned.