Note:  Do not rely on this information. It is very old.


Boundary, in Geometry, means the geometrical entity that separates any other geometrical entity from its surroundings. The four geometrical entities usually dealt with are solids, surfaces, lines, and points. A solid is bounded by surfaces, a surface by lines, and a line by points. If the surfaces bounding a solid be given, the solid is completely determined. But given the close curve bounding a surface, we may obtain an infinite number of other surfaces with the same boundary. So also an infinite number of different lines may be bounded by the same two points. [Geometry.]