Design principles are ideas that guide developers toward certain goals in software design.
Software has many different desirable quality aspects -- among them are reliability, security, maintainability, efficiency, and size; and these are all impacted by choices made by the developers. Software design principles tend to focus on the maintainability aspects of quality: is the code loosely coupled, or does it have many dependencies that make it hard to use? Is the code highly cohesive, or is a collection of unrelated information needed to use a module? Is the code readable and understandable? Is the code testable? Is the code usable and reusable? Is the code simple or complex?
Various design principles can be used by developers to advise them in making choices that will yield highly cohesive, loosely coupled, simple, maintainable designs. The SOLID design principles are an example of specific design advice for object oriented projects. The Principles of User Interface Design provide design advice for creating user interfaces.
