OpenTelemetry is an open source project that provides tools to collect telemetry data like traces, metrics, and logs to analyze application behavior and performance. It provides a standard way to collect telemetry data across different technologies. The document discusses using OpenTelemetry in .NET applications, including adding the necessary packages, configuring logging, and exporting telemetry data to the console. It highlights advantages like easy implementation, integration with other tools via exporters, good community support, and minimal performance impact.