Geometry Vocabulary/Definitions (3rd grade)

Terms	Definitions
Square	A quadrilateral with 4 equal sides and 4 right angles. Opposite sides are parallel.
Rectangle	A Quadrilateral with 4 sides and 4 right angles. Opposite sides are parallel.
Triangle	A polygon with 3 sides and 3 angles.
Circle	A polygon made with a continuous line which is always the same distance from the center.
Line	A straight path that goes without end in two directions.
Ray	Part of a line that has one end point and goes in one direction without end.
Line Segment	Part of a line with two end points.
Angle	Two rays with the same end point.
Right Angle	An angle that is 90 degrees (It makes a square in the corner).
Side	Line segments of a polygon.
Vertex	The point where two sides meet. (Shared end points of the line segments of a polygon.)
Quadrilateral	A polygon with 4 sides and 4 angles.
Parallelogram	A quadrilateral (4 sides & 4 angles) where opposites sides are parallel. (ie: Rectangle, square, rhombus, & diamond are parallograms)
Trapezoid	A quadrilateral (4 sides & 4 angles) with one pair of parallel sides.
Rhombus	a parallelogram with four equal sides and equal opposite angles.
Equilateral triangle	A triangle that has 3 equal sides.
Isosceles Triangle	A triangle that has 2 equal sides.
Right Triangle	A triangle that has one right angle. It can also be an isosceles or scalene triangle.
Scalene Triangle	A triangle that has no equal sides. All 3 sides are different lengths.
Congruent	A plane figure with the same size and shape.
Symmetry	A plane figure that can be folded along a line so the two parts match.
Line of Symmetry	The line that divides two matching parts. It can be vertical, horizontal, or diagonal.
Perimeter	The distance around the figure.
Area	The size a surface takes up, measured in square units.
Rectangular Prism	A solid shape that has: 6 faces (4 rectangles & 2 squares), 8 vertices (corners), and 12 equal edges.
Cube	A solid shape that has: 6 square faces all equal in size, 8 vertices (corners), and 12 equal edges.
Sphere	A solid shape that is perfectly round like a ball. No faces, edges, or vertices.
Cone	A solid shape with a circular base and a curved surface that come to a point (vertex).
Cylinder	A solid shape with one curved surface and two congruent circular bases.
Pyramid	A solid shape with a polygon as a base and triangular faces that come to a point (vertex or apex)
Volume	The amount of space occupied by a 3D object, measured in cubic units.
Face	The flat surface of a 3D shape.
Edge	Where two surfaces join (intersect).
Plane	A flat surface.
Plane shape	A flat closed shape having only 2 dimensions.
Plane figure	A flat figure that can be closed or not closed.