Geometry
Shapes, angles, triangles, circles, area, volume, coordinate geometry, proofs, and transformations.
Angles & Lines49
Types of angles, angle relationships, parallel lines, transversals, and perpendiculars
Area & Perimeter17
2D measurement formulas for area and perimeter of common shapes
Circles25
Circle properties, arcs, sectors, chords, tangent lines, and inscribed angles
Geometric Transformations17
Reflections, rotations, translations, dilations, and isometries in geometry
Geometry Foundations18
Foundational geometry concepts, planes, measurement units, non-Euclidean geometry, and general vocabulary
Platonic Solids & Polyhedra20
Regular polyhedra, Euler's formula for polyhedra, and special 3D shapes
Quadrilaterals & Polygons33
Quadrilaterals, regular polygons, and their properties
Surface Area & Volume54
3D measurement: surface area and volume of prisms, cylinders, cones, spheres, and other solids
Triangles & Congruence67
Triangle types, congruence tests, special lines in triangles, and triangle properties
Logic & Proof1
Conditional statements, proof methods, logical connectives, and quantifiers
Geometric Constructions1
Geometry Constructions1
3d Geometry0
Graph Transformations & Symmetry2
All Geometry Terms A–Z (269)
- AA Similarity
- AAS Congruence
- Acute Angle
- Acute Triangle
- Adjacent
- Adjacent Angles
- Alternate Angles
- Alternate Exterior Angles
- Alternate Interior Angles
- Altitude
- Altitude of a Cone
- Altitude of a Cylinder
- Altitude of a Parallelogram
- Altitude of a Prism
- Altitude of a Pyramid
- Altitude of a Trapezoid
- Altitude of a Triangle
- Angle
- Angle Bisector
- Angle of Depression
- Angle of Elevation
- Angle Sum Property of a Triangle
- Annulus
- Apex
- Apothem
- Arc of a Circle
- Area of a Circle
- Area of a Convex Polygon
- Area of a Kite
- Area of a Parabolic Segment
- Area of a Parallelogram
- Area of a Rectangle
- Area of a Regular Polygon
- Area of a Rhombus
- Area of a Sector of a Circle
- Area of a Segment of a Circle
- Area of a Trapezoid
- Area of a Triangle
- Area of an Ellipse
- Area of an Equilateral Triangle
- Arm of an Angle
- ASA Congruence
- Axis of a Cylinder
- Axis of Reflection
- Axis of Rotation
- Base
- Base of a Trapezoid
- Base of a Triangle
- Base of an Isosceles Triangle
- Between
- Bisect
- Bisector
- Cavalieri's Principle
- Center of Rotation
- Centers of a Triangle
- Central Angle
- Centroid
- Centroid Formula
- Ceva's Theorem
- Cevian
- Cevian Theorem
- Chord
- Circle
- Circular Cone
- Circular Cylinder
- Circumcenter
- Circumcircle
- Circumference
- Circumscribable
- Circumscribed
- Coincident
- Collinear
- Complement of an Angle
- Complementary Angles
- Compression of a Geometric Figure
- Concave
- Concentric
- Concurrent
- Cone
- Cone Angle
- Congruence Tests for Triangles
- Congruent
- Consecutive Interior Angles
- Convex
- Coplanar
- Corresponding
- CPCFC
- CPCTC
- Cube
- Cylinder
- Decagon
- Degree
- Diagonal of a Polygon
- Diameter of a Circle or Sphere
- Diametrically Opposed
- Dihedral Angle
- Dilation of a Geometric Figure
- Disk
- Dodecagon
- Dodecahedron
- Edge of a Polyhedron
- Elliptic Geometry
- Equiangular Triangle
- Equidistant
- Equilateral Triangle
- Euclidean Geometry
- Euler Line
- Euler's Formula (Polyhedra)
- Exterior Angle of a Polygon
- Exterior Angle Theorem
- Face of a Polyhedron
- Fixed
- Fractal
- Frustum of a Cone or Pyramid
- Geometric Figure
- Geometry
- Glide Reflection
- Golden Mean
- Golden Rectangle
- Golden Spiral
- Great Circle
- Heptagon
- Heron's Formula
- Hexagon
- Hexahedron
- HL Congruence
- HL Similarity
- Horizontal
- Hyperbolic Geometry
- Hypotenuse
- Icosahedron
- Image of a Transformation
- Incenter
- Inradius
- Inscribed Angle in a Circle
- Inscribed Circle
- Interior
- Interior Angle
- Invariant
- Isometry
- Isosceles Trapezoid
- Isosceles Triangle
- Kite
- Lateral Surface
- Lateral Surface Area
- Leg of a Right Triangle
- Leg of a Trapezoid
- Leg of an Isosceles Triangle
- Line
- Line Segment
- Linear Pair of Angles
- Major Arc
- Measure of an Angle
- Median of a Trapezoid
- Median of a Triangle
- Mensuration
- Midsegment
- Minor Arc
- Minute
- Möbius Strip
- n-gon
- Net (Geometry)
- Non-Adjacent
- Non-Euclidean Geometry
- Nonagon
- Noncollinear
- Oblique Cone
- Oblique Cylinder
- Oblique Prism
- Oblique Pyramid
- Obtuse Angle
- Obtuse Triangle
- Octagon
- Octahedron
- Orthocenter
- Parallel Lines
- Parallel Planes
- Parallel Postulate
- Parallelepiped
- Parallelogram
- Pentagon
- Perimeter
- Perpendicular
- Perpendicular Bisector
- Plane
- Plane Figure
- Plane Geometry
- Platonic Solids
- Point
- Polygon
- Polygon Interior
- Polyhedron
- Pre-Image of a Transformation
- Prism
- Pyramid
- Pythagorean Identities
- Pythagorean Theorem
- Pythagorean Triple
- Quadrilateral
- Radian
- Radius of a Circle or Sphere
- Ray
- Rectangle
- Rectangular Parallelepiped
- Regular Polygon
- Regular Prism
- Regular Pyramid
- Rhombus
- Right Angle
- Right Circular Cone
- Right Circular Cylinder
- Right Cone
- Right Cylinder
- Right Prism
- Right Pyramid
- Right Regular Prism
- Right Regular Pyramid
- Right Square Prism
- Right Triangle
- Rotation
- SAS Congruence
- SAS Similarity
- Scale Factor
- Scalene Triangle
- Secant Line
- Second
- Sector of a Circle
- Segment of a Circle
- Self-Similarity
- Semicircle
- Semiperimeter
- Side of a Polygon
- Similar
- Similarity Tests for Triangles
- Skew Lines
- Slant Height
- Solid
- Solid Geometry
- Sphere
- Square
- SSA
- SSS Congruence
- SSS Similarity
- Straight Angle
- Supplement
- Supplementary Angles
- Surface
- Surface Area
- Takeout Angle
- Tangent Line
- Tessellate
- Tetrahedron
- Three Dimensions
- Torus
- Transversal
- Trapezium
- Trapezoid
- Triangle
- Triangle Inequality
- Triangulation
- Truncated Cone or Pyramid
- Truncated Cylinder or Prism
- Undecagon
- Varignon Parallelogram of a Quadrilateral
- Vertex
- Vertical
- Vertical Angles
- Volume
- Zero Dimensions
Frequently Asked Questions
What is geometry?
Geometry is the branch of mathematics concerned with the properties, measurement, and relationships of points, lines, angles, surfaces, and solids.
What is the difference between Euclidean and non-Euclidean geometry?
Euclidean geometry is based on flat surfaces where parallel lines never meet. Non-Euclidean geometries (like spherical or hyperbolic) relax this assumption, allowing for curved spaces where parallel lines can converge or diverge.
What are the most important geometry formulas?
Key formulas include: area of a triangle (½ × base × height), Pythagorean theorem (a² + b² = c²), circumference of a circle (2πr), area of a circle (πr²), and volume of common solids like cylinders (πr²h) and spheres (4/3 πr³).