If I was going to actually try to define “flight” it would be more complicated than the idea intuitively feels. Should it include a paper airplane, or a party balloon, or a rocket operating in vacuum? What about a submarine, it relies on buoyancy sure but is otherwise kinda similar to a propeller plane? What is the cutoff between flight and swimming, is it defined by Reynold’s number? Does it even make sense to describe the actions of birds and airplanes using the same short english word, would humans seeing both for the first time (Plato’s cave style) cluster them together that way?
Intelligence is the same but more so, because it is more multifaceted, more abstract, less directly observable. I suspect the only reason we can even roughly measure human and animal intelligence now is that all biological intelligence evolved under similar goals/constraints, survival and reproduction in whatever the local environment is, usually using biological sensing and motive equipment with some kind of analogs in our own bodies. When we create narrow AI systems they are truly alien, and don’t work that way, so to us they don’t look like our intuitive understanding of intelligence.* But we can still make some instinctive comparisons. I don’t know if Deep Blue is smarter than a high frequency trading algorithm, but Watson or a self driving car probably is. Luckily, humanity does have at least a small community of researchers actually trying to answer the question of what intelligence is.
*Among other reasons, such systems might be intelligent but are not sentient or sapient - they like feelings or self-awareness, neither of which I can adequately define but which certainly play a role in my estimates of the intelligence of other humans.
If I encountered a program that could converse with me smoothly in natural language, learn to play a new game I brought it given the official rules, explain why it took various actions, ask probing questions, and surprise me with new insights, I would admit it is intelligent. Not saying those are all necessary, but together I would probably find them sufficient - though only as long as the system was not specifically designed to pass such a test, I expect that would be game-able. But if, say, a future iteration of IBM Watson, designed as a tool set for use in many applications, could also readily do this, I would credit it with intelligence.
