Pack-fresh describes a card that's in the same condition it was in when it came out of the pack — untouched, unhandled, and showing no signs of wear whatsoever. It's the hobby's way of saying "this card has been pristine since the moment it was pulled."
A pack-fresh card should have sharp corners, clean edges, a flawless surface, and solid centering. It's the kind of condition that gives you the best shot at a high grade if you submit it for grading.
When sellers describe a card as "pack-fresh," they're telling you it went straight from the pack into a sleeve and toploader without being mishandled. It's a trust signal — though you should always verify condition yourself before buying.