It's a complicated question since depending on the theory you use, the definition of intelligence change. The IQ is getting more and more controversed. Another concept is intelligence split in 8 sphere, (i don't recall all of them but for exemple music is one of them) being intelligent would mean to have an easier time acquiring skills in this field or to have accumulated a vast ammount of knowledge.

Let's just say that there isn't a global consensus on what define intelligence yet.

Imo, inteligence is the ability to relate information and get the results you want. A good chess player remembers how I move and is able to use that to move the situation towards his prefered state (winning).

Google "theory of multiple intelligences", it describes different areas where one can be proficient. For example, logical reasoning, social skills, music, etc. Noone has ever created a good metric for "general inteligence" or how smart you are in total, and it is debated if such a thing even makes sense.

This statement. although 25+ years old, is still pretty good.

If you take a whole bunch of things that people have to learn to do (e.g. maths, spelling, logic, speed of thought, and memory), they all correlate pretty well together. So psychologists call this statistical manifold "g" for "general intelligence".

Theories like Gardner's multiple intelligences are frankly nonsensical because it ignores statistical reality, and replaces the word "talent" or "ability" with "intelligence". Thus he refers to intelligent (meaning good) dancers with a straight face.

The biological basis of intelligence is largely unknown, although brain size, number of neurons, and amount of folding is correlated.

Cognitive abilities like how much you can hold in your working memory, and how quickly you can make decisions, although correlate and plausibly cause intelligence differences.