Ellipse

A plane curve surrounding two focal points, such that for all points on the curve, the sum of the two distances to the focal points is a constant.

Equilateral

An equilateral triangle has sides of equal length. All its three angles are 60 degrees.

Excircle

An excircle or escribed circle of the triangle is a circle lying outside the triangle, tangent to one of its sides and tangent to the extensions of the other two.

Golden ratio

If something is divided in two parts such that the proportion of the smaller part to the larger equals the proportion of the larger to the whole.

Height

The height of a polygon is the perpendicular distance of the base to the furthest corner.

Hexagon

A polygon with six sides

Hyperbola

A hyperbola is a set of points whose difference of distances from two foci is a constant value.

Hypotenuse

The hypotenuse is the longest side in a right triangle. It lies opposite the right angle.

Incentre

The point of a triangle where the three angle bisectors cross. It is equidistant from all the sides. It is also the centre of the inscribed circle.

Incircle

The incircle or inscribed circle of a triangle is the largest circle that can be contained in the triangle