A segment is a group of your users defined by rules that you set. Users are automatically added to the segment every time the user updates to match those rules. Segments are different to tags, in that users need to be added to tags manually and tag members are not automatically managed.
The API supports fetching the list of segments created in your App, however creating and managing segments must be done through Intercom. For more information about segmenting users, please see the product documentation.