A solid with four triangular faces. A regular tetrahedron has faces that are equilateral triangles. Plural: tetrahedra.
Theorem
A mathematical statement derived from previously accepted premises and established by means of a proof. A 'theory' is slightly different - this is a testable model that can be used to make predictions, but isn't yet proven.
Translation
In geometry, a type of transformation in which every point of a shapemoves the same distance in the same direction; a transformation that is specified by a distance and direction (vector).
Trapezium
A quadrilateral with exactly one pair of sides parallel.
Tree Diagram
A branching, decision diagram in which probabilities may be assigned to each branch and used to determine the probability of any outcome of combined or compoundevents.
Triangle
A polygon with three sides. Adjective: triangular, having the form of a triangle.