The ellipse has two principal lines which are at right angles
and bisect each other. One determines its maximum 'length' and is known as the major axis. The other
is the minimum 'width' and is known as the minor axis. Each axis is also a line of symmetry.
The 'centre' of an ellipse is the point where the two axes cross. There
are also two points which lie on the major axis, and are at equal distances from the centre, known as the foci ('foe-sigh'). The distance between these two points is the foci distance.
The eccentricity of an ellipse is a measure of how fat (or thin) it is. Its value can vary from 0 to 1. A value of 0 (major and minor are equal in length) indicates it is a circle. A value of 1 means the minor axis does not exist,
i.e. its is a a straight line. The ellipse belongs to a family of curves known as the 'conic sections'.
The circle is considered as a special case of ellipse.