Tool calling
Also called: function calling
In one sentence
The mechanism by which a model requests that an external function be run on its behalf.
In more depth
The model does not execute anything itself. It emits a structured request naming a tool and its arguments; the surrounding program decides whether to run it, runs it, and returns the result into the context.
That gap is the control point. Every meaningful permission decision about an agent lives in the code that chooses whether to honour a tool request.