Segment object
A Segment is one unit of data from a provider, in effect a key and a value, such as membership in an audience or a contextual category. Segments sit in the segment array of a Data object, and the exchange must publish segment IDs, names, and possible values to buyers in advance.
How it is used
A segment ID means something only within its provider's namespace, so buyers always read it together with the parent Data.id or Data.name. Most traffic sends IDs alone.
Fields
Where it sits
Contained in: Data.
All objects
The field reference index lists every OpenRTB 2.x object.