Nowadays you can create Permanent, Transient or Segment audiences with Convert Experiences. Permanent and Segment Audiences work the same way as they did prior to April 2019, but Transient Audiences are new.
This type of audience is checked only at visitor bucketing time and will not be checked again on their subsequent visits. If the audience conditions are met by the visitor, the Experience will run. If the audience conditions are not met anymore by the visitor on subsequent visits, it will not cause the Experience to be stopped for that visitor.
For example, if you define an audience for a specific hour and minute, e.g. hour 12 and minute 5, and when you visit the page the hour is 12 and the minute is 3, the permanent audience conditions will not be matched and the Experience will be skipped (screenshot was taken from Google Chrome console while the Convert Experiences Debugger is ON):
If the permanent audience conditions were matched, then the Experience will randomly decide which variation to present to you:
If after a few minutes you try again, because audience conditions were checked previously for you and a variation was served, the same variation will still be served to you, even though you are outside of the correct minutes (as defined in the audience conditions).
With this audience type, audience conditions will be re-checked each time an experience is to be presented (versus the Permanent ones that will only be checked at visitor bucketing time).
For example, if you define an audience for a specific hour, e.g. 9, and when you visit the page the hour is 11, the transient audience conditions will not be matched and the experiment will be skipped:
If you define an audience for a specific hour, e.g. 11, and when you visit the page the hour is 11, the transient audience conditions will be matched and the experiment will run:
If you then open another tab after the Experience had already decided which variation to serve to you, transient audience conditions will be checked again. If they still match, it will serve you the same variation that was presented before:
If you visit again, perhaps an hour later where transient audience conditions no longer match, the Experience will be skipped.
Segments are a group of visitors that qualify for some Audience conditions (such as location, device used to access the site, hour of the day, and any other visitor behaviors) and can be used at a later time for targeting. Visitors in a specific segment may be likely to behave or purchase in the same way. Thus, you can create segments by defining audience conditions that allow Convert Experiences to determine which segment a visitor qualifies for and run the appropriate variation.
A segment basically allows a visitor to qualify for an audience on subsequent visits even if they do not meet the audience conditions on those subsequent visits. That is why we call segments persistent. This means that if a visitor qualifies for such an audience in the first visit, he will continue to qualify for that audience every time he visits the page. If he visits multiple times, sometimes meeting the conditions and sometimes not, he will keep seeing the Experience regardless of the current matching.
Not attached to any experiment
You can also create an Audience that you would designate as a Segment and not attach to any Experience. Visitors who match the audience condition will be collected in this Segment, even if the Segment has not been added to any Experience. Later on, you can use this Segment in an Experience, which will add previously collected (as well as newly-matching) "segmented" visitors, when they visit and also match the Site Area conditions of an Experience.
Segments are evaluated at the Project level, so any visitor that reaches a page with the Project tracking code and who matches the Audience conditions designated as a Segment will be added to it.
Saved Segments in a Project can be used on other Experiences in that Project as well.
You can read more about Segments here.