A triangle is a polygon with three corners and three sides, one of the basic shapes in geometry. The corners, also called vertices, are zero-dimensional points while the sides connecting them, also called edges, are one-dimensional line segments. The triangle's interior is a two-dimensional region. Sometimes an arbitrary edge is chosen to be the base, in which case the opposite vertex is called the apex.
The Flatiron Building in New York is shaped like a triangular prism
In geometry, a polygon is a plane figure made up of line segments connected to form a closed polygonal chain.
Historical image of polygons (1699)
The Giant's Causeway, in Northern Ireland