Synthesis, association, the ability to marry different abstract concepts to create a more accurate map of reality. That, to me, is what I would call intelligence. Say you're designing a wing for a car, well if you have questions about aero, you ask a bird, they live all their life flying. How do you ask a bird? You present a problem and observe how they solve it. Now, that's great you have some insight, but how do you apply that to a car? A bird wants to fly so it creates lift, to make a car go faster, we need to create negative lift, so you have to invert the design. You also have to consider cars have things like tires and weigh a hell of a lot more than a bird. Yet somehow you can still take inspiration from nature and birds and apply that knowledge to designing parts to make cars go faster around corners. To me, that synthesis and adaptation is intelligence. Or if you're trying to learn something but the language is foreign but the pronunciation is close enough to one of the languages you already know, which helps you memorize and later translate what you heard. That ability to piece together a coherent picture from limited inputs, and still be roughly on point, that to me, is intelligence. Like a great detective that pays attention to all the details and all the sequences of events to arrive at the correct outcome. That synthesis, to me is a mark of intelligence.