At my dance studio they are making a pom line and I'm kinda confused of what it is. Like what do they do?

Semi-formal basically means "as formal as you can be without wearing a tuxedo".

Wear a suit, button-down shirt, tie, and shoes to match. Simplest suit to wear is grey, but any colour (navy, tan, black etc.) will do. The shirt should be white or have a simple pattern, but if you're adventurous you can get a way with something a little more interesting. The tie should match the suit - dark suit/dark tie, light suit/light tie, but again you can be flexible. Wear socks that basically match the colour of the suit trousers - your socks should look like an extension of your pant leg. Go with black shoes if you're wearing grey or black suit, brown shoes if you're wearing tan.

Avoid the jeans/blazer look. Be colourful if you feel like it. Wear a tie ,but not a garish one. Cufflinks are a good accessory.