# Glossary

apex
in a pyramid, the vertex at which all lateral faces meet

base
in a prism, the two congruent, parallel faces at the top and bottom; in a pyramid, the regular polygon that is not a lateral face

congruent
having the same size and shape

cube
a polyhedron with six congruent, square faces

cylinder
a three-dimensional object with circular bases

dodecahedron
a polyhedron with 12 congruent, pentagonal faces

edge
the segment along which two faces meet

Euler's Theorem
for any polyhedron, the sum of the number of vertices and faces is equal to two more than the number of edges; stated another way, F + V - E = 2

face
one of the surfaces of a polyhedron

height
the distance from top to bottom of a three-dimensional figure

icosahedron
a polyhedron with 20 congruent, triangular faces

lateral face
in a prism, one of the rectangles that connects the bases to one another; in a pyramid, one of the triangles that connects the base to the apex

length
the longest dimension of a solid figure; for a three-dimensional figure, it is usually the distance from front to back

octahedron
a polyhedron with eight congruent, triangular faces

polygon
a two-dimensional figure formed by connecting three or more straight line segments end to end (triangles, squares, and hexagons are examples of polygons)

polyhedron
a three-dimensional figure whose faces are polygons

prism
a three-dimensional figure with two parallel, congruent bases connected by rectangles

rectangular prism
a prism whose bases are rectangles; in general, a prism can be described by the shape of its bases

right prism
a prism in which the bases meet the lateral faces at right angles

tetrahedron
a polyhedron with four congruent, triangular faces

truncated icosahedron
a polyhedron with 32 faces, 12 of which are pentagons and 20 of which are hexagons

vertex vertices[plural]
the point at which three or more faces meet

width
distance from side to side