subroutine

In computer programming, a subroutine is a sequence of program instructions that perform a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed.

Advantage : 1- Code reuse  2- Modification and Maintenance of Code becomes easy. 

A subroutine is often coded so that it can be called several times and/or from several places during one execution of the program, including from other subroutines, and then branch back (return) to the next instruction after the call once the subroutine's task is done.