Modular programming

Modular programming divides software into independent units with specific responsibilities and defined interfaces. Modules can be developed, tested, and changed with limited effects on one another.

Software module: A software unit that groups related functionality behind a defined boundary. Modules are the units that modular programming organizes into a larger program.
Dependency inversion principle: A design principle that makes high-level policy depend on abstractions rather than concrete low-level details. Depending on abstractions can prevent module boundaries from being tied to specific implementations.
Structured programming: A programming approach that organizes control flow using sequence, selection, and iteration rather than arbitrary jumps. Structured programming addressed complexity in control flow, while modular programming addressed organization across units.
Monolithic architecture: A software architecture in which an application is built and deployed as one integrated unit. A monolith may have internal modules, but it lacks the same independently deployable boundaries as separate services.
Plugin architecture: A software design that lets optional components add features through defined extension points. Plugins are modules designed to be added or removed without rewriting the host application.
Module interface: The operations and data a software module exposes to other modules. A clear interface lets modules interact without depending on internal details.
Dependency injection: A technique that supplies an object or component with its dependencies from outside. Supplying dependencies externally makes module implementations easier to replace and test.
David Parnas: A computer scientist known for foundational work on information hiding and software module design. Parnas articulated how to choose module boundaries around design decisions likely to change.
Microservices: An architectural style that organizes an application as independently deployable services communicating over a network. Microservices apply modular boundaries across processes, adding deployment and communication costs.
Shared library: A compiled library that multiple programs can load and use at runtime. Shared libraries package reusable functionality behind a binary interface.

Linked from 2 pages

Modular designBroader topic: It applies modular design directly to the organization of source code.