It's a profesional grading service. If they are PSA the cards get put into a large hard plastic slab with a grade from 1 to 10 on the label. You cannpt open the slab up unless you break it. I'm guessing your cards are all raw (aka ungraded).
Here is a link to their website and you can see a picture of what the PSA cards look like in their slabs.
https://www.psacard.com/
