Object-Oriented Software Analysis and Design (OOSAD) is a methodology used to design and develop software systems by modeling them as a collection of interacting objects. These objects represent real-world entities, encapsulating data (attributes) and behavior (methods). The approach emphasizes principles like abstraction, inheritance, polymorphism, and encapsulation to enhance modularity, reusability, and maintainability. OOSAD typically follows a lifecycle that includes requirements gathering, analysis, design, implementation, and testing. It employs visual modeling tools like Unified Modeling Language (UML) to create diagrams that illustrate system structure and behavior, such as class diagrams, sequence diagrams, and use case diagrams. This methodology is widely used in complex, large-scale projects due to its ability to simplify system complexity by focusing on the relationships and interactions among objects.