In 3D modeling, a line set defines which edges are rendered as strokes in a non-photorealistic style

https://wiki-square.win/index.php/HVAC_Line_Set_Replacement_Warning_Signs_You_Shouldn%E2%80%99t_Ignore

In 3D modeling, a line set defines which edges are rendered as strokes in a non-photorealistic style, controlling visibility, crease emphasis, silhouette extraction, and intersection highlights for stylized visuals.