Audiences help you show an experiment or campaign to a specific group of visitors who come to your site, based on conditions that you specify. For example, you might want your experiment to target visitors who've seen a specific AdWords campaign. Or, you might show an experiment to visitors on mobile devices only. Audiences help you do that.
The following examples shows visitors you can include or exclude:
Visitors using certain browsers or devices
Visitors who come from certain sources (like an AdWords campaign, a Google search, or a Facebook ad)
Visitors who have certain cookies
Visitors who come to your page with certain query parameters (like
Visitors with browsers set to certain geographical areas or languages
You can create an audience that captures that information about your visitors and add it to an experiment, so only those visitors who meet those conditions are eligible to enter. You can also use AND and OR conditions to combine multiple audiences together for more specific targeting conditions in a specific experiment.
Audiences are evaluated each time the experiment is due for activation which means a visitor may satisfy the audience and be included in the experiment some times but not others. For example, the "time of day" audience condition will only qualify visitors during a time period specified.
Visitors who do not meet your audience conditions are not included in an experiment or campaign. They are excluded from your experiment and just see the usual experience on your site. They also are not included in the experiment's count of unique visitors on the Results page.
Audiences determine who can see the experiment. If you want to control where on your site the experiment will run, see URL Targeting: Choose where your experiment runs
If you are using Optimizely Web Experimentation, check out the audience conditions you can use to group your visitors into an audience.