What is a self-contained block of code that can be reused in other programs called?

The term that refers to a self-contained block of code that can be reused in other programs is a module library. A module library is designed to encapsulate specific functionality that can be used across multiple programs, allowing developers to write code more efficiently by avoiding duplication and promoting code organization. By using a module library, programmers can easily include and invoke the contained functions or classes in their projects, enhancing code maintainability and modularity.

The term "function call" refers to the process of executing a specific block of code that is defined elsewhere, but it does not encompass the concept of being a self-contained reusable component on its own. "Code snippet" typically describes a small portion of reusable code that might serve a specific purpose but lacks the broader organizational structure associated with libraries. "Class definition" refers to a blueprint for creating objects in object-oriented programming, but like a function call, it does not imply the broader context of reusability afforded by a module library. Therefore, the most fitting answer in this context is the module library, as it embodies the idea of a structured collection of reusable code components.