Covers 11 fundamental system design concepts including scalability (horizontal vs vertical), throughput vs bandwidth, concurrency vs parallelism, CAP and PACELC theorems, latency reduction techniques (caching, sharding, load balancing), database types (SQL vs NoSQL), transaction models (ACID vs BASE), and API architectural styles (REST, SOAP, GraphQL). Explains how these concepts help engineers design systems that handle millions of users while maintaining performance and reliability.