Geometry Vocabulary

acute angle

An angle that measures less than 90 degrees.

acute triangle

A triangle with all angles measuring less than 90 degrees.

angle

A figure formed by two rays sharing a common endpoint called the vertex.

complementary angle

Two angles whose measures add to 90 degrees.

congruent

Figures with the same size and shape.

correspondence

The relationship between two or more objects that are matched.

equilateral triangle

A triangle with three congruent sides.

isoscleles triangle

A triangle with at least two congruent sides.

line

A straight path that extends without end in opposite directions.

line symmetry

One half of a figure is a mirror image of the other half.

line of symmetry

The imaginary line drawn down the center of a figure with line symmetry.

obtuse angle

An angle whose measure is greater than 90 degrees.

obtuse triangle

A triangle containing one obtuse angle.

parallel lines

Lines in a plane that never intersect.

parallelogram

A quadrilateral with two pairs of parallel sides.

perpendicular lines

Lines that intersect to form right angles.

plane

A flat surface that extends forever.

point

An exact location in space.

polygon

A closed figure formed by three or more line segments that intersect only at their endpoints.

ray

A part of a line that starts at one endpoint and extends forever in one direction.

rectangle

A parallelogram with four right angles.

reflection

A transformation of a figure that flips the figure across a line.

regular polygon

A polygon with congruent sides and angles.

regular tessellation

A regular polygon is repeated to fill a plane.

rhombus

A parallelogram with all sides congruent.

right angle

An angle that measures 90 degrees.

right triangle

A triangle containing a right angle.

rotation

A transformation in which a figure is turned around a point.

rotational symmetry

A figure can be rotated less than 360 degrees around a central point and coincide with the original figure.

scalene triangle

A triangle with no congruent sides.

segment

A part of a line between two endpoints.

square

A rectangle with four congruent sides.

supplementary angles

Two angles whose measures have a sum of 180 degrees.

tesselation

A repeating pattern of plane figures that completely cover a plane with no gaps or overlaps.

transformation

A change in the size or position of a figure.

translation

A movement of a figure along a straight line.

transversal

A line that intersects two or more lines.

trapezoid

A quadrilateral with exactly one pair of parallel sides.

Triangle Sum Theorem

The theorem that states that the measures of the angles in a trianlge add up to 180 degrees.

vertical angles

A pair of opposite congruent angles formed by intersecting lines.

corresponding angles

Angles formed by a transversal cutting through 2 or more lines that are in the same relative position.

quadrilateral

A four sided figure

pentagon

A five sided figure

hexagon

A six sided figure

heptagon

A seven sided figure

octagon

An eight sided figure