Changes can be starred with labels that behave like private hashtags. Any label can be applied to a change, but these labels are only visible to the user for which the labels have been set.
The star REST API supports:
Only the default star is shown in the WebUI and can be updated from there. Other stars do not show up in the WebUI.
If the default star is set by a user, this user is automatically notified by email whenever updates are made to that change.
The default star is the star that is shown in the WebUI and which can be updated from there.
The default star is represented by the special star label 'star'.
If the ignore star is set by a user, this user gets no email notifications for updates of that change, even if this user is a reviewer of the change or the change is matched by a project watch of the user.
Since changes can only be ignored once they are created, users that watch a project will always get the email notifications for the change creation. Only then the change can be ignored.
Users that are added as reviewer to a change that they have ignored will be notified about this, so that they know about the review request. They can the decide to remove the ignore star.
The ignore star is represented by the special star label 'ignore'.
There are several query operators to find changes with stars:
Star labels cannot contain whitespace characters. All other characters are allowed.
Part of Gerrit Code Review