In a system design interview, you will be asked to design a complex system, such as a website, mobile app, or network infrastructure. The interviewer will evaluate your ability to decompose the problem into smaller subproblems, make trade-offs between different design decisions, and consider the scalability and performance of the final solution. The key to success in a system design interview is to clearly communicate your thought process and trade-offs, rather than getting bogged down in low-level implementation details.