Segment definitions
Whether created using the API or using the Segment Builder, segment definitions are ultimately defined using Profile Query Language (PQL). This is where the conceptual segment definition gets described in the language built to retrieve profiles meeting the criteria. For more information, see the PQL overview.
To learn how to create and use segments in the Segment Builder (the UI implementation of Segmentation Service), see the Segment Builder guide.
For information on building segment definitions using the API, see the tutorial on creating segment definitions using the API.
Reference: https://experienceleague.adobe.com/en/docs/experience-platform/segmentation/home