In other words, Barry Allen no longer needs to use an extrapolator to see Kara and vice-versa.
Apparently, this was always the end goal of Crisis on Infinite Earths.
Even though in the comics, Earth-Prime is our Earth, I just personally like the sound of Earth-Prime.

Colin Bentley/The CW
So all of the CW [superhero] shows will be on the same Earth.
In fact, the Arrowverse starts embracing the possibilities of Earth-Prime in tonights episode.
And Earth-Prime isnt the only change.
Earth-19:Home of the shortlivedSwamp Thingseries on DC Universe.
Earth-9:Home of DC UniversesTitans, which was renewed for a third season last year.
Earth-96:Brandon Rouths Man of Steel fromSuperman Returnlives!