##### Geometry Vocabulary

Quadrilateral

a closed two-dimensional shape with four straight sides

Rhombus

a parallelogram with four congruent sides

Square

a rectangle with four congruent sides

Rectangle

a parallelogram with four right angles

Parallelogram

a quadrilateral with two pairs of parallel sides

Trapezoid

a quadrilateral with exactly one pair of parallel sides

Isosceles Triangle

a triangle with at least two sides of the same length

Scalene Triangle

a triangle with no sides of the same length

Equilateral Triangle

a triangle with three sides of the same length

Acute Angle

an angle that measures less than ninety degrees

Right Angle

an angle that measures exactly ninety degrees

Obtuse Angle

an angle that measures more than ninety degrees and less than one hundred eighty degrees

Reflex Angle

an angle that measures more than one hundred eighty degrees

Polygon

a closed two-dimensional shape made from line segments that do not cross each other

Concave Polygon

a polygon for which you can connect two points inside the polygon with a line segment that passes outside the polygon

Convex Polygon

a polygon that is not concave and all the inside angles have a measure less than 180 degrees

Pentagon

a five sided polygon

Hexagon

a six sided polygon

Octagon

an eight sided polygon

Regular Polygon

a polygon in which all sides and all angles are congruent

Congruent

exactly equal in size and shape (sides, angles and figures can be congruent)

Obtuse Triangle

a triangle with an obtuse angle

Acute Triangle

a triangle with three acute angles

Straight Angle

an angle that measures exactly one hundred and eighty degrees

Perpendicular

lines or segments that intersect to form right angles (or a square corner)

Parallel

lines or segments that stay the same distance apart and never meet or cross

Horizontal

parallel to the horizon of the earth

Vertical

perpendicular to the horizon of the earth

Point

an exact location in space

Line

a straight path that extends forever in opposite directions; named by two endpoints

Line Segment

a part of a line with two endpoints; named by the two endpoints

Ray

a part of a line with one endpoint that extends forever in one direction

Vertex

the point on an angle or polygon where two lines or rays meet

Intersecting

lines or segments that meet or cross at one point

Right Triangle

a triangle with one right angle

One-Dimensional

a figure with only one dimension, usually length

Two-Dimensional

a figure with two dimensions, usually length and width

Three-Dimensional

a figure with three dimensions, usually length, width and height

Face

a flat surface of a three-dimensional figure

Edge

a line segment where two faces of a three-dimensional figure meet

Cube

a box-shaped solid figure that has six identical square faces

Rectangular Prism

a solid figure with two rectangular bases that are congruent and parallel