Semicircle

A circle cut in half along its diameter.

Similar

Two objects are similar of they have the same shape, but not necessarily the same size.

Tangent

The line that touches a curved two-dimensional object, such as a circle, in just one point. A tangent to point on a circle is perpendicular to the radius to that tangency point.

Tetrahedron

A three-dimensional object having four triangular faces, six straight edges and four vertices.

Translational symmetry

Invariance of an object if translated or slided.

Trapezium

A quadrilateral with at least one pair of parallel sides. Also known as trapezoid.

Unit circle

A circle with radius 1.

Vector

An object that has a magnitude (length) and direction. Vector algebra is widely used in physics.

Vertex

A point where two lines, curves or edges meet.