The ability of a language model to identify when a request requires invoking an external tool or API, generating the structured call (function name and parameters) instead of just free text. The actual execution of the function happens outside the model.
In GENAI-L (Domains 2 and 3) this is the technical mechanism that lets Gemini act as an agent: it decides which function to call (e.g. checking inventory, scheduling an appointment), the application executes that function, and returns the result to the model so it can continue the conversation.
Function calling is a concept that can show up on the exam. Check the full guide to see it in context.