Water migration is the movement of water away from its initial source through or along materials, gaps and building pathways.
What this means at your property
A leak above a room may become visible at a ceiling joint some distance away. Flooring edges or framing can also carry water into adjoining areas. The visible stain is therefore a clue to investigate, not a reliable map of the entire loss.
What should the assessment record?
Ask for the suspected source, confirmed affected locations and any inaccessible layers. Tracking those distinctions helps explain why the repair boundary may change when further access or measurements reveal additional moisture.