They attempt to measure the theoretical concept of generalized intelligence, known by psychometricians as g. They're obviously not perfect, but they're better than anything else we have.
>People who score high on IQ tests do take IQ tests (or similar puzles on a daily basis).
not necessarily, on an official test, I scored 140 (which I'd consider high), and I don't do any puzzles or similar at all.
that said, obviously an IQ test is not perfect, but, I'd argue a high score is a good indication that a person is relatively intelligent. Middle scores and below can be attributed to a lot of other things (distractions, etc etc), but, the high score is still indicative of your brains capabilities. If that made sense?
> I don't really know what IQ is supposed to measure
Neither does anyone else.