The bubble () was a forum post icon used by the members of the following modding teams involved in the beatmap ranking process:
Being the next step of the old ranking system after a proto-bubble, a regular bubble meant that a beatmap was ready to be ranked from the modder's point of view. Bubbled beatmaps would be eventually checked by another member of the BAT or BN and ranked or approved as long as only minor changes to the map were required.
See also: Mapping and modding timeline
Bubbles were introduced by peppy on October 29, 2007, for "beatmaps that are being considered for ranked play (pending further moderator's feedback)". Setting a beatmap thread's icon to a bubble was a way for BAT members to indicate that the beatmap was of good quality and had followed the ranking criteria.
On October 3, 2010, the MAT received the permissions to use the bubble icon, alongside the BAT. This essentially deprecated the proto-bubbles, and both teams had been primarily using regular bubbles since.
After the beatmap discussion system was fully implemented and became the main interface for modding in November 2017, the forum-based beatmap management controls were phased out, with bubbles being naturally replaced by nominations.
List of bubbled beatmaps, followed by popped bubbles and starred maps
An existing bubble could be popped:
In both cases, the beatmap thread's icon would be set to a popped bubble (). If a bubble was popped manually, it was assumed that the BAT or MAT member who placed the icon would ensure that the necessary changes were made to the map before it continued in the ranking process.