Adjacent Sides  -  Sides of a polygon that share a vertex.

Base  -  One of the parallel sides of a trapezoid.

Center of a Regular Polygon  -  The point on the interior of a polygon from which all vertices of the polygon are equidistant.

Closed Curve  -  A curve whose starting point is the same as its ending point.

Concave Polygon  -  A polygon with one or more interior angles greater than 180 degrees.

Congruent Polygons  -  Polygons whose sides are all congruent

Consecutive Vertices  -  Vertices of a polygon that include the endpoints of the same side.

Continuous  -  Without any gaps or holes.

Convex Polygon  -  A polygon whose interior angles are all less than 180 degrees.

Consecutive Angles  -  Angles in a polygon that share a segment as one of the sides that could be extended into a ray.

Curve  -  An arrangement of continuous points in space.

Decagon  -  A ten-sided polygon.

Diagonal  -  A line segment joining nonconsecutive vertices of a polygon.

Dodecagon  -  A twelve-sided polygon.

Equiangular Polygon  -  A polygon whose angles are congruent.

Equilateral Polygon  -  A polygon whose sides are congruent.

Exterior Angle  -  The angle formed at a vertex of a polygon that lies outside of the region enclosed by a polygon.

Heptagon  -  A seven-sided polygon.

Hexagon  -  A six-sided polygon.

Interior Angle  -  The angle formed, at a vertex of a polygon, that lies inside the region enclosed by the polygon.

Leg  -  One of the nonparallel sides of a trapezoid.

Median  -  The segment in a trapezoid whose endpoints are the midpoints of the legs of the trapezoid.

Nonagon  -  A nine-sided polygon.

Opposite sides  -  Sides of a quadrilateral that don't share a vertex.

Octagon  -  An eight-sided polygon.

Parallelogram  -  A quadrilateral with two pairs of parallel sides.

Pentagon  -  A five-sided polygon.

Polygon  -  A simple closed curve consisting of the union of segments that intersect each other at their endpoints.

Quadrilateral  -  A four-sided polygon.

Rectangle  -  A quadrilateral with four congruent angles.

Regular Polygon  -  An equilateral, equiangular polygon.

Rhombus  -  A quadrilateral with four congruent sides.

Side  -  One segment that comprises part of a polygon.

Simple Closed Curve  -  A closed curve that does not intersect itself.

Square  -  A quadrilateral with four congruent sides and angles.

Trapezoid  -  A quadrilateral with one pair of parallel sides.

Triangle  -  A three-sided polygon.

Vertex  -  The common endpoint of two sides of a polygon.