Geometry Vocabulary Flashcards
Free geometry vocabulary flashcards with plain-language definitions for basic terms, angles, triangles, quadrilaterals, circles, transformations and solid shapes. Flip each card, mark what you know and keep drilling the terms you miss.
Keys: Space or Enter flips, arrow keys move, K marks known, R marks review. No sign-up and nothing is stored.
How to study with these geometry vocabulary flashcards
- Read the front of the card and say or write your answer before you flip it.
- Flip the card, then mark I know this only if you were right without hesitating.
- Mark Review again for anything you missed, then use Review missed only to drill those cards.
- Pick one topic at a time, then shuffle all topics for a mixed review.
All 68 cards at a glance
Every card is also listed below so you can scan, print or review without the viewer.
Basic terms
| Question | Answer |
|---|---|
| Point? | An exact location with no size, usually named with a capital letter. |
| Line? | A straight path that goes on forever in both directions. |
| Line segment? | Part of a line with two endpoints. |
| Ray? | Part of a line with one endpoint that goes on forever in one direction. |
| Plane? | A flat surface that extends forever in all directions. |
| Collinear points? | Points that lie on the same line. |
| Coplanar points? | Points that lie in the same plane. |
| Parallel lines? | Lines in the same plane that never meet. |
| Perpendicular lines? | Lines that meet at a right angle (90°). |
| Midpoint? | The point that divides a segment into two equal parts. |
| Bisector? | A line, ray or segment that divides something into two equal parts. |
| Congruent? | Having the same size and shape. |
| Similar figures? | Figures with the same shape and proportional sides, but not necessarily the same size. |
Angles
| Question | Answer |
|---|---|
| Acute angle? | An angle less than 90°. |
| Right angle? | An angle exactly 90°. |
| Obtuse angle? | An angle greater than 90° and less than 180°. |
| Straight angle? | An angle exactly 180°. |
| Reflex angle? | An angle greater than 180° and less than 360°. |
| Complementary angles? | Two angles whose measures add to 90°. |
| Supplementary angles? | Two angles whose measures add to 180°. |
| Adjacent angles? | Angles that share a vertex and a side but do not overlap. |
| Vertical angles? | Opposite angles formed by two intersecting lines. They are equal. |
| Transversal? | A line that crosses two or more other lines. |
| Corresponding angles? | Angles in matching positions at each intersection of a transversal. Equal when the lines are parallel. |
| Alternate interior angles? | Angles between the two lines on opposite sides of a transversal. Equal when the lines are parallel. |
Triangles
| Question | Answer |
|---|---|
| Equilateral triangle? | A triangle with three equal sides (and three 60° angles). |
| Isosceles triangle? | A triangle with at least two equal sides. |
| Scalene triangle? | A triangle with no equal sides. |
| Right triangle? | A triangle with one 90° angle. |
| Hypotenuse? | The longest side of a right triangle, opposite the right angle. |
| Median of a triangle? | A segment from a vertex to the midpoint of the opposite side. |
| Altitude of a triangle? | A perpendicular segment from a vertex to the opposite side (or its extension). |
| Centroid? | The point where the three medians meet. |
| Circumcenter? | The point where the perpendicular bisectors meet; the center of the circle through all three vertices. |
| Incenter? | The point where the angle bisectors meet; the center of the inscribed circle. |
| Congruence shortcuts for triangles? | SSS, SAS, ASA, AAS and HL (for right triangles). |
Quadrilaterals and polygons
| Question | Answer |
|---|---|
| Polygon? | A closed flat shape made of straight line segments. |
| Regular polygon? | A polygon with all sides equal and all angles equal. |
| Parallelogram? | A quadrilateral with two pairs of parallel sides. |
| Rectangle? | A parallelogram with four right angles. |
| Rhombus? | A parallelogram with four equal sides. |
| Square? | A shape that is both a rectangle and a rhombus. |
| Trapezoid? | A quadrilateral with at least one pair of parallel sides. |
| Kite? | A quadrilateral with two pairs of equal adjacent sides. |
| Convex polygon? | A polygon in which every interior angle is less than 180°. |
| Diagonal? | A segment joining two non-adjacent vertices of a polygon. |
Circles
| Question | Answer |
|---|---|
| Radius? | A segment from the center to a point on the circle. |
| Diameter? | A chord through the center; twice the radius. |
| Chord? | A segment with both endpoints on the circle. |
| Tangent? | A line that touches a circle at exactly one point. |
| Secant? | A line that intersects a circle at two points. |
| Arc? | A part of the circumference of a circle. |
| Sector? | A region bounded by two radii and an arc. |
| Central angle? | An angle whose vertex is the center of the circle. |
| Inscribed angle? | An angle whose vertex is on the circle and whose sides are chords. |
| Circumference? | The distance around a circle. |
Transformations and solids
| Question | Answer |
|---|---|
| Translation? | Slides a figure without turning or flipping it. |
| Reflection? | Flips a figure over a line. |
| Rotation? | Turns a figure around a fixed point. |
| Dilation? | Enlarges or shrinks a figure by a scale factor from a center. |
| Symmetry? | When a figure can be folded, flipped or turned so that it matches itself. |
| Prism? | A solid with two parallel congruent bases and rectangular faces. |
| Pyramid? | A solid with one polygon base and triangular faces meeting at an apex. |
| Cylinder? | A solid with two parallel circular bases. |
| Cone? | A solid with one circular base and a curved surface that comes to a point. |
| Sphere? | A set of points in space that are all the same distance from the center. |
| Face, edge and vertex of a solid? | A face is a flat surface, an edge is where two faces meet, and a vertex is where edges meet. |
| Euler’s formula for polyhedra? | V − E + F = 2 |
Frequently asked questions
What is the difference between a rhombus and a square?
A square is a special rhombus with four right angles. Every square is a rhombus, but not every rhombus is a square.
What is the difference between complementary and supplementary angles?
Complementary angles add to 90° and supplementary angles add to 180°. A memory trick is that C comes before S, and 90 comes before 180.
Which geometry words appear most on tests?
Parallel, perpendicular, congruent, similar, bisector, median, altitude, tangent, chord and the angle names appear most often in basic geometry courses and standardized tests.
Sources
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