SQL Server is a relational database management system (RDBMS) developed by Microsoft for Windows and Linux. It uses Transact-SQL (T-SQL), which can be compiled into batches of statements that SQL Server caches to improve query performance. The system allows configuration of resource use, including memory, CPU, and storage allocation through resource pools, virtual instances of SQL Server that access a slice of their parent's resources. Key metrics for monitoring include batch requests per second, last elapsed time, SQL compilations per second, SQL recompilations per second, buffer cache hit ratio, page life expectancy, checkpoint pages per second, used memory, CPU usage percentage, disk read and write I/Os per second, page splits per second, avg_fragmentation_in_percent, user connections, and system resource utilization. Monitoring these metrics can help diagnose issues with query performance, resource allocation, and database fragmentation, enabling optimization of SQL Server configurations for improved visibility into databases.