Software structuring in assembly and high-level languages: A small program unit written once and invoked multiple times from different places in a larger program is commonly called a(n) ________.

Introduction / Context:
Code reuse and modularity are central to software engineering. In assembly and higher-level languages alike, programmers encapsulate a repeated operation in a callable unit so that it is written once and used many times, reducing duplication and improving maintainability.

Given Data / Assumptions:

• The construct can be invoked from multiple points in the program.
• Control returns to the caller after execution (unless specified otherwise).
• It may use parameters and return values or registers according to calling conventions.

Concept / Approach:
The standard term for such a reusable program unit is “subroutine.” In various languages, equivalent terms include function, procedure, method, or routine. In assembly, CALL transfers control to the subroutine; RET returns to the caller, often using the stack for return addresses and parameters.

Step-by-Step Solution:

Verification / Alternative check:
Programming texts and ABIs define subroutines with calling conventions (parameter passing, register saving, return values).

Why Other Options Are Wrong:

Common Pitfalls:
Confusing interrupts with normal calls; mixing “macro” (textual expansion) with subroutines (single copy executed via call).

Final Answer:
subroutine