Lunar node
In plain words
One of the two places where the Moon's path crosses the Sun's. They matter because eclipses can only happen near them.
In the tradition's terms
The intersections of the lunar orbit with the ecliptic — the north node ascending, the south descending.
In depth
Retrograde through the zodiac at about 19.3° a year, completing a circuit in 18.6 years — the rhythm the eclipse seasons keep. The Oracle computes the true node from the orbital state vector, not the smoothed mean.