Design Nomenclature / Form & Geometry
Edge
Also called boundary edge, open edge, border edge, segment
The straight segment between two vertices, and the unit that carries a mesh's structure. How many faces share an edge classifies it: exactly two is manifold interior, one is a boundary edge, three or more is non-manifold. An edge holds no position of its own — moving a vertex moves every edge on it.
In practice
'Open edge' or 'border' for the one-face case; it is what a slicer reports as a hole, and what a border-select finds. Hard and soft edges are a shading attribute, not a structural one.