It's a plane figure bounded by 3 straight lines that intersect at 3 vertices
[DOC] [TLE] Geometry Glossary - McRae Family Website [PAR] area - the surface enclosed within a closed plane figure; the measure of the 
surface, ... ball - a "solid sphere"; the interior of a sphere (open ball); a sphere 
and its ... central angle of a circle - an angle whose vertex is the center of the 
circle .... polygon - a union of 3 or more line segments where each segment 
intersects 2 other... [DOC] [TLE] Polygon - Wikipedia [PAR] In elementary geometry, a polygon /pln/ is a plane figure that is bounded 
by a finite chain of straight line segments closing in a loop to form a closed chain 
or circuit.