A subroutine is part of a program that performs a specific task & can be actioned from more than one place within the program. For instance, in a windows program the programmer may write a subroutine to close the current window as this task is likely to be actioned from several different places within the program.
SUBROUTINE
Meaning of SUBROUTINE in English
English glossary of Internet and PC terminology. Английский глоссарий Интернет и ПК терминологии. 2012