Kusto Query Language (KQL) is a read-only query language developed by Microsoft for analyzing large volumes of structured, semi-structured, and unstructured data. Named after oceanographer Jacques Cousteau, it powers Azure Data Explorer, Azure Monitor Logs, Azure Sentinel, Microsoft 365 Defender, and Application Insights. KQL is optimized for telemetry, metrics, logs, and time-series analysis, providing powerful operators for aggregation, filtering, visualization, and machine learning directly in the query layer. Unlike SQL, KQL is declarative and designed for fast, interactive data exploration with a pipe-based syntax that flows data transformations left-to-right. Understanding KQL's tabular operators, scalar functions, and query optimization patterns is essential for security analysts, data engineers, and cloud practitioners working with Microsoft's data analytics ecosystem.

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