Tool Use
Also called: Function Calling, Tool Calling
Tool use is a model calling external software during a task: querying a database, sending an email, running a calculation, or reaching another system through its API. The model does not execute the code. It is given a list of available functions and, when it judges one to be needed, asks for that function to be called with particular arguments; the surrounding software runs the call and hands the result back for the model to continue with. This is the capability that separates a system which writes about an action from one that performs it.
In practice
Every tool you connect is a permission you have granted, and a model that can send an email can send the wrong one to the wrong list. Scope tool access the way you would scope a service account and log every call, because the question after an incident is which action the model took, not what it said.