AFAIK, it used to be known as function calling, but with newer model updates and the introduction of the Assistants API, it has been renamed to tool calling for consistency and clarity. This is evident from the API reference where the functions parameter has been deprecated in favor of the tools parameter, and function_call in favor of tool_choice.
If you mean regarding chat completion (wasn’t sure what is ‘complication’ and thought maybe autocorrect): function call was the original api attribute but it is now deprecated in favor of tools.
This post has more information about what is different: blocking you from using a role message as you wish, placing extra tokens into context out of your control…
The huge jump in tokens when the AI uses this wrapper tool