Geometry

Geometry is a branch of mathematics that deals with shapes and their properties - points, lines, planes and solids.

Geometry Terms

  • Acute angle - An angle that measures less than 90°.
  • Adjacent angle - Two angles on a plane having the same vertex and a common line.
  • Angle - Two rays sharing a common point.
  • Angle bisectors - A line that divides an angle into two equal angles.
  • Apex - The vertex at the tip of a cone or pyramid.
  • Apothem - A line segment from the center of a regular polygon to the mid point of a side.
  • Arc length - The distance along the arc or the circumference of a circle or any curve.
  • Area - The inside space of a figure.
  • Base - The bottom of a figure in either plane or solid geometry.  If the bottom and top are parallel then either can be called base.
  • Base area - The base surface area of a solid figure.
  • Center of a circle - A point at a fixed equal distance from all points of the circumference of a circle.
  • Central angle - An angle in a circle with the vertex at the circle's center.
  • Centroid - The center of a plane or mass.
  • Chord - A line segment on the interior of a circle.
  • Circle segment - An interior part of a circle bound by a chord and an arc.
  • Circumcircle - A circle that passes through all the vertices of a two-dimensional figure.
  • Circumference - The outside of a circle or a complete circular arc.
  • Concave - An internal angle is greater than 180°.
  • Congruent - All sides having the same lengths. All angles measure the same.
  • Conic section - A section on any plane through a circle, ellipse, hyperbola, and parabola.
  • Convex - No internal angle is greater than 180°.
  • Coplanar - Lines or points lying on the same plane.
  • Diagonal - A line from one vertices to another that is non adjacent.
  • Edge - A line where two or more vertices come together.
  • Ellipsoid - A three-dimensional figure sphere like surface for which all cross sections are ellipses.
  • Foci - Two fixed points on the interior of an ellipse used to define the curve.
  • Focus - The points that construct a conic section.
  • Geometric figure - Any set of points on a plane or in space.
  • Horizontal - Flat or level.
  • Hyporenuse - The side of right triangle opposite the right angle, which is the longest side.
  • Inradius - A circle that touches all lines of a figure.
  • Inscribed angle - An angle inside a circle with its vertex in the circle.
  • Inscribed circle - The largest circle possible that can fit on the inside of a two-dimensional figure.
  • Interior angle - An angle on the interior of a plane figure.
  • Lateral surface area - The surface area of a solid figure excluding the area bases of the solid figure.
  • Line - A straight path connecting two points.
  • Line segment (segment) - All points bertween two points.
  • Locus - A word used to define a set of points that form a geometric figure or graph.
  • Median - A line segment from a vertex (corner point) to the midpoint of the opposite side.
  • Oblique - Tilted at an angle, not horizontal or vertical.
  • Oblique cone - A three-dimensional figure with the apex not alligned above the center at 90° to the base.
  • Oblique cylinder - A three-dimensional figure with both bases not alligned above each other and the center not at 90° to the other base center.
  • Oblique prism - A three-dimensional figure with both bases not alligned above each other and the center not at 90° to the other base center.
  • Oblique pyramid - A three-dimensional figure with the apex not alligned above the center at 90° to the base.
  • Obtuse angle - An angle that measures more than 90°.
  • Outradius (circumcircle) - A circle that touches all corners of an figure.
  • Parallel lines - Two lines that do not intersect.
  • Parallel planes - Two planes that do not intersect.
  • Perimeter - The sum of the lengths of all sides of a plane figure.
  • Perpendicular - At a 90° angle.
  • Perpendicular bisector - A line perpendicular to a segment passing through the segment's midpoint.
  • Plane - An infinate expanse of points in two directions.
  • Point - A single location or the intersection of two lines.
  • Polyhedron - A three-dimensional figure that is a solid with no curved edges or sides.
  • Porportional - Having a constant ratio.
  • Pyramid - A three-dimensional figure that is a polyhedron with a polygonal base and lateral faces that taper to an apex.
  • Quadrilateral - A polygon with four sides.
  • Radius - A line segment between the center point and a point on a circle or sphere.
  • Ray - A line starting at a point and extending infinitely in one direction.
  • Rectangular angle - Two rectangles with different lengths that intersect at a 90° angle at one end each.
  • Regular hexahedron - A three-dimensional figure that is a regular polyhedron where all faces are squares.
  • Regular pentagon - A two-dimensional figure that is a polygon with five congruent sides.
  • Regular polygon - A two-dimensional figure that is a polygon where all sides are congruent and all angles are congruent.
  • Regular polyhedron - A three-dimensional figure having faces that are all congruent regular polygons and has dihedral angles that are all congruent.
  • Regular prism - A three-dimensional figure having a base that are regular polygons.  The base is not necessarily aligned one above the other.
  • Regular pyramid - A three-dimensional figure having a base that are regular polygons.  The apex is not necessarily above the center of the base.
  • Regular right prism - A three-dimensional figure having a base that are regular polygons.
  • Regular right pyramid - A three-dimensional figure having a base that are regular polygons.
  • Right angle - A 90° angle.
  • Right cone - A three-dimensional figure with the apex directly above the center at 90° to the base.
  • Right cylinder - A three-dimensional figure with both bases directly above each other and having the centers at 90° to each others base.
  • Right prism - A three-dimensional figure with both bases directly above each other and having the centers at 90° to each others base.
  • Right pyramid - A three-dimensional figure with the apex directly above the center at 90° to the base.
  • Secant line - A line that passes through at least two points on a curve.
  • Sector of a circle - A sector is a fraction of the area of a circle with a radius on each side and an arc.
  • Semi-perimeter - One half of the perimeter.
  • Side - Any line segment of an figure.
  • Surface - A three-dimensional figure excluding internal points.
  • Surface area - The total area of all the surfaces of a three dimensional figure.
  • Three-dimensional - A figure with height, width, and depth.
  • Two-dimensional - A flat figure.
  • Vertex - A point where two or more curves, edges, or lines meet.
  • Vertical - Straight up and down.
  • Vertical angles - The opposite angles when two lines intersect.
  • Volume - The amount of space in an solid figure.
Display #
Title
Acute Angle
Angle
Angle Types
Apex
Apothem
Area
Arm of an Angle
Base
Chord of a Circle
Congruence of Segments
Congruent Angles
Congruent Complementary
Congruent Right Angle
Congruent Supplements
Congruent Vertical Angles
Diagonal
Edge
Euclid's Postulates
Exterior Angles
Face
Geometry Terms
Heron's Formula
Interior Angles
Leg
Line Segment

Subcategories