Are these good everyday socks or just for the holidays?

They are novelty Christmas socks, so the print limits them to seasonal wear. The fine knit and stretch blend make them comfortable enough for a full day, but most people treat them as holiday-only.

Will they fit someone who wears a size 9 shoe?

They are sized for men's 10-13, so a size 9 foot will likely find them loose. The spandex helps them grip, but the fit is cut for larger feet.

No. They are a polyester and spandex blend, which is why the print stays crisp and the sock stretches. That blend breathes less than cotton.

What does 200 needle construction mean?

It refers to the number of needles on the knitting machine. A higher count gives a finer, denser stitch, which feels smoother and holds shape better than coarse novelty socks.