Basic Geometry Vocabulary Review

Plane and Solid Figures Plane figure – a plane figure has just 2 dimensions – length and width. Solid figure – a solid figure has 3 dimensions – length, width, and height.

Solid Figures Face – each flat surface of a solid figure Edge – a line segment where 2 faces meet on a solid figure. Vertex – “a corner” – where 3 or more edges meet. The plural form of vertex is “vertices.”

Solid Figures

Polygons Polygon – a polygon is a closed plane figure made up of line segments. Each line segment is a side.

Polygons – Know Your Prefixes! “Tri” – means 3 – a triangle has 3 sides. “Quad” – means 4 – a quadrilateral has 4 sides. “Penta” – means 5 – a pentagon has 5 sides. “Hexa” – means 6 – a hexagon has 6 sides. “Hepta” – means 7 – a heptagon has 7 sides. “Octa” – means 8 – an octagon has 8 sides. “Nona” – means 9 – a nonagon has 9 sides. “Deca” – means 10 – a decagon has ten sides.

Points, Lines, Line Segments, and Rays Point – an exact location in space. Line – a straight path of points that goes on and on in two directions. Line segment – a part of a line. It has 2 endpoints. Ray – part of a line. It has one endpoint and continues on and on in only one direction.

Angles Right angle – has a square corner Acute angle – less than a right angle Obtuse angle – more than a right angle. Straight angle – forms a straight line.

Lines Parallel lines – never intersect. Intersecting lines – lines that cross through the same point. Perpendicular lines – lines that form right angles where they intersect each other.

Quadrilaterals Quadrilaterals can also be classified (or grouped) by their angles or their pairs of sides! Remember , quad means 4! So we are talking about 4 sided figures!

Rectangle Rectangle – there are 4 right angles!

Square Square – there are 4 right angles and all sides are the same length.

Trapezoid Trapezoid – There is only one pair of parallel sides.

Parallelogram Parallelogram – opposite sides are parallel.

Rhombus Rhombus – opposite sides are parallel AND all 4 sides are the same length.

Congruent Congruent – Same shape and same size. *If items are congruent, they are automatically similar. However, just because items are similar, doesn’t mean they are automatically congruent.

Slide (Translation) Slide (translation) – moves a figure in a straight direction.

Flip (Reflection) Flip (reflection) – a figure gives its mirror image.

Turn (Rotation) Turn (rotation) – moves a figure around a point.

Similar Similar – same shape, but may or may not have the same size! *If items are congruent, they are automatically similar. However, just because items are similar, doesn’t mean they are automatically congruent.

Symmetry Symmetry – when a figure can be folded into two congruent halves. *Means one half can lay perfectly over the other half in an exact match. line of symmetry