angle - Two rays with a common endpoint called a vertex.

area - The number of square units needed to cover a given space.

complementary angle - Two angles whose measures have a sum of 90 degrees.

congruent - Equal.

degree - A unit for measuring angles.

geometry - A branch of mathematics that deals with the measurement, properties, and relationships of points, lines, angles, surfaces, and solids.

intersecting lines - Lines that cross at one point.

isosceles - A triangle with two congruent sides.

length - The longer or longest dimension of an object.

obtuse angle - An angle that measure more than 90 degrees but less than 180 degrees.

parallel lines - Lines in the same plane that never intersect.

parallelogram - A quadrilateral with opposite sides parallel.  Each pair of opposite sides and angles are congruent.

perimeter - The distance around a polygon.

plane - A flat surface extending in all directions.

point - An exact location in space.

polygon - A closed plane figure made up of line segments.

puzzle - To solve with difficulty or ingenuity.

quadrilateral - A polygon with fours sides and four angles whose sum is 360 degrees.

ray - A part of a line that has one endpoint and extends in one direction without end.

rectangle - A parallelogram with four right angles.

right angle - An angle that measures 90 degrees.

rotation - A transformation obtained by rotating a figure a given turn angle about a point.

shapes - To give a particular form or shape to.

similarity - The quality or state of being similar.

square - Having four equal sides and four right angles.

supplementary angles - Two angles whose measures have a sum of 180 degrees.

symmetry - Correspondence in size, shape, and relative position of parts on opposite sides of a dividing line or median plane or about a center of axis.

tangram - A Chinese puzzle made by cutting a square of thin material into a number of pieces which can be recombined into many different figures.

triangle - A polygon having three sides.

vertex - A point where two or more rays meet, where sides of a polygon meet, or where edges of a polyhedron meet.

width - A distance from side to side.