It means you can expect the stable One UI update for the Note 9. Samsung has released the stable One UI update for the Galaxy S9 series after 4th One UI update. It also brings the January 2019 security patch.
The update is currently rolling out with build version N960FXXU2ZRLT, while the size of the update is 123.12 MB.
If you have installed the beta build on your Galaxy Note 9, you can check for the update manually by heading into the Settings > Software updates > Download updates manually. This will allow the software to update and load the beta version.