As with the eggshell category the amount of shine in a semi-gloss will vary depending on store but essentially semi-gloss is semi-gloss and is typical for trim and doors. One exception for doors is exterior doors. I like to use eggshell on them if they are in direct sun because the sheen of the semi-gloss will dull everywhere except where the weather stripping sits and that will stay nice and shiny so every time you open the door you will see a shiny frame and it will remind you that you need to paint your door! Keep in mind that semi-gloss (and gloss) don’t cover as well as the lower sheens so you may need an extra coat.
Gloss is good for pianos, cars and nails. I have maybe used it 2 times in the 20 years I have owned my business. It hurts my eyes and the surface has to be perfect for it to look good.