Buffer Overflow Intro. ©2002, Jedidiah R. Crandall, Susan L. Gerhart, Jan G. Hogle.  http://sfsecurity.pr.erau.edu
Programmers use subroutines for common functions used many places

Alice breaks her program into subroutines. 

Subroutine R might invoke (or call) subroutine S which invokes (calls) subroutine T.  When T is finished Norman needs to resume with subroutine S, and when S is finished he needs to resume where he left off in subroutine R.