Semantic Kernel is a lightweight, open-source development kit that lets you easily build AI agents and integrate the latest AI models into your C#, Python, or Java codebase. It serves as an efficient middleware that enables rapid delivery of enterprise-grade solutions, backed with security enhancing capabilities like telemetry support.
Semantic Kernel combines prompts with existing APIs to perform actions. By describing your existing code to AI models, they’ll be called to address requests. When a request is made the model calls a function, and Semantic Kernel is the middleware translating the model's request to a function call and passes the results back to the model.
source: https://learn.microsoft.com/en-us/semantic-kernel/overview/