A useful reference of geometric terms and their definitions.

**Attributes and Spatial Properties **

Qualities (usually used with geometry) of a figure, including sides, size, angles, etc.

**Angle:**Two lines that meet to make a corner.**Congruent:**Identical in size and shape.**Dimensions/Size:**Terminology to describe the dimensions of an object or set. With young children, the terms*large, medium, small, taller, shorter, longer, less than*and*greater than*are all appropriate.**Edge:**The meeting of two faces on a three-dimensional shape.**Face:**Surface planes of three-dimensional shapes.**Flat:**Having a plane-like quality.**Equilateral:**Sides that are the same length.**Location terms:**Words and phrases that describe the location of an object in relation to other objects, including words like*on*,*under*,*on top of*,*next to*,*in front of*,*behind*,*beneath*,*underneath*,*inside*,*outside*,*at/on the bottom/top*,*between*, and*adjacent to*(this is just a sample, there are many more).**Parallel**: Two lines in a two-dimensional space that do not meet (for example, the opposite sides of a square). A parallelogram has two sets of parallel lines.**Plane:**A flat two-dimensional surface upon which two-dimensional objects (e.g., circle, square) can lie, or the face of a three-dimensional object as it creates a surface (e.g., face of a cube); the dimensions of which are infinite.**Point:**A specific position on a line, plane, or in space.**Pointy:**An informal word to describe angles of objects.**Side**: Line segments in geometric figures that compose the exterior of the object.**Straight:**Without a curve.**Vertex/Vertices:**Also known as corner/corners. The point at which two sides of a two-dimensional figure or two edges of a three-dimensional figure meet.**Wavy:**Having curvy or undulating attributes (e.g., ocean, octopus tentacles).

**Two-Dimensional Figures**

**Circle**: A two-dimensional shape in which all points on the curved line are equidistant from a center point.**Triangle:**A closed figure with three sides.**Rectangle:**A two-dimensional, closed, four-sided figure with four right angles.**Rhombus:**A closed four-sided figure with parallel opposite sides. A square is a special kind of rhombus. Sometimes called a*diamond*.**Square:**A special type of rectangle that has equilateral (same length) sides and parallel opposite sides.**Pentagon:**A closed figure with five sides.**Hexagon:**A closed figure with six sides.**Septagon/Heptagon:**A closed figure with seven sides.**Octagon:**A closed figure with eight sides.

**Three-Dimensional Figures**

**Cube:**A three-dimensional figure with identical equilateral squares as faces (a cube is also a*prism*, see*square prism*below).**Sphere:**A round body whose surface is at all points equidistant from the center.**Cone:**A solid or hollow object that tapers from a circular or roughly circular base to a point.**Pyramid:**A three-dimensional figure on which the faces are triangular and converge to a single point at the top. Pyramids are named after the shape of their base (triangular pyramid, square pyramid, rectangular pyramid).**Prism:**A three-dimensional figure with identical ends. Named after the two-dimensional shape at the ends. For instance, a rectangular prism has identical rectangles at each end. A hexagonal prism has identical hexagons at each end: triangular prism, square prism (also called a*cube*), rectangular prism, pentagonal prism, hexagonal prism, heptagonal prism, octagonal prism.

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