We don't need a clear and unambiguous definition of intelligence in order to tell that other human beings are intelligent.
The problem here is that not every human being is intelligent and yes, we are actually trying to define intelligence through IQ tests, for example.
Likewise, we don't need one in order to start trying to create an artifice that impresses us into thinking it also is intelligent.
So when you need accounting software you say: "write me something that will be as clever as my accountant". Is that the way you formulate tasks for software engineers?