SOLID is a set of five timeless principles that help developers write better, more reliable object-oriented code.SOLID stands for: Single Responsibility Principle, Open-Closed Principle, Liskov Substitution Principle, Interface Segregation Principle, and Dependency Inversion Principle.These principles were introduced by Robert C. Martin (Uncle Bob) to improve code quality and maintainability.The Single Responsibility Principle states that every class should have one responsibility, encapsulated within the class.