What does ‘Mesh has uncovered edges’ warning mean?
 

Hi, I’ve been creating a mesh in ICEM, but when I try to convert the mesh to unstructured and save it, it says

‘Warning: Mesh has uncovered edges. Ansys fluent needs a complete boundary (lines in 2D) or it will give a variety of errors and not read the mesh. If this was 2D Hexa, perhaps your edges are not associated with perimeter curve’?

What does this mean please?

Thanks in advance