The North and South Node (The Nodal Axis )

A Moon's node (North or South Node) is either of the two orbital nodes of the Moon, that is, the two points at which the orbit of the Moon intersects the ecliptic; the great circle that is the apparent path of the Sun among the constellations in the course of a year; from another viewpoint, the projection on the celestial sphere of the orbit of Earth around the Sun. The constellations of the zodiac are arranged along the ecliptic. The North Node is where the Moon moves into the northern ecliptic hemisphere while the descending or South Node is where the Moon enters the southern ecliptic hemisphere. The Nodal Axis is the line between the North Node and the South Node. They are not two separate and independent points - like all the four axes of Diamond Astrology - but an axis that has an interaction between both poles. 

The South Node reveals a central theme of the past that is likely to reach a point of saturation in your life. It also represents a talent. 
The North Node is the call of your Soul, the invitation for growth to step into a new field of consciousness, which pushes your nose towards the future. 

The Nodal Axis represents a process in your life along which you will both integrate and stagnate, which depends on the aspects your Nodal Axis makes in your chart and on the Progressions and Transits.