The parameter FLOW can be applied for ARC and POLYGONS (but not for vector points) and it means the label position can FLOW to a better position when dragging the map. For example, the name of a lake polygon can automatically reposition to remain fully visible when only a portion of the lake remains visible in the map view. (So the label placement does not simply reflect the polygon centroid position).
The allowed label position can be specified by mixing several parameters, such as:
LabelPosition := [gisLabelPositionUpright, gisLabelPositionDownright];
The label FLOW parameter is exposed as a setting in the visual layer property control.