Pozyx positioning solutions always consist of at least two parts: anchors and tags. Anchors are modules with a fixed and known position. The anchors have the same role as satellites in GPS positioning. The tags by the same analogy can be thought of as the GPS system in your car although their exact relation varies on the used protocol (TWR/TDOA or RTDOA).
One thing that is always consistent however, is that anchors are always static (their relative position towards other anchors stays the same) and tags are dynamic. The tags’ positions are computed based on time of flight measurements between anchors (of which the position is known) and tag.