It's a relative abstract measure of case size that's the same across experience levels. A junior and a senior should both be able to agree that a given case is small/medium/large relative to the kind of cases their team usually handles, even if the case would take two hours for the senior and two weeks for the junior. Story points codify small/medium/large into numbers (Fibbonacci is a common choice, like 1, 2, 3, 5, 8, 13, where 13 is often "too big for one sprint").

Mapping story points to time doesn't really work for individual cases because of those different experience levels, it's going to heavily depend on who does the case. Instead, you track story points competed in total for the team for the entire sprint - the different experience levels average out into something consistent, like 30-35 story points per sprint.

"Velocity" is related scrum terminology, and is the mapping of that whole-team measure back to time. A previous team that understood how this worked and stuck to it had those story points per two-week sprints, so we could estimate things months out with reasonable accuracy despite the different skill levels.

I also thought this post was going to be about story points because it's a common complaint from people who don't understand the "different experience levels" part. If everyone on the team reliably took the same amount of time for a given case, then yeah, you could cut it out and just estimate in time. But it's not for that.