The SOLID principles are a set of five software design principles that promote the creation of clean, maintainable, and scalable code.

These principles were introduced by Robert C. Martin in his book «Agile Software Development, Principles, Patterns, and Practices» and are fundamental to object-oriented software engineering:
The SOLID principles provide clear guidelines for software design that favor the creation of more robust, flexible, and easy-to-maintain systems over time. Understanding and applying these principles in object-oriented software development is essential to improve code quality and efficiency.
