Design patterns are recommended practices that solve recurring design problems in software systems, with four parts: name, problem description, solution, and consequences. The master data-lookup pattern is a popular technique used to improve application performance, especially for long-lived, infrequently changing data such as country lists, genres, and movie languages. This pattern involves accessing master data quickly and efficiently, often using Redis, which can speed up access and manipulation operations while preserving data consistency. By applying this pattern, developers can create faster response times and improve the overall performance of their MEAN and MERN stack applications.