Performance Optimization and Query Tuning refer to improving the efficiency and speed of database queries and data processing systems. It involves analyzing query execution plans, identifying bottlenecks, and rewriting queries for better performance. Techniques include indexing, partitioning, caching, and optimizing joins and filters. Query tuning helps reduce resource usage, execution time, and system load while improving response time. It is essential in large-scale databases, data warehouses, and cloud platforms like Snowflake and SQL-based systems. Performance Optimization and Query Tuning ensure faster data retrieval, better scalability, and efficient system performance in enterprise environments.