The Pāta, or lunar nodes, are the orbital nodes of the Moon on the Celestial sphere, that is, the points where the path of the Moon crosses the ecliptic. The ascending node is where the moon crosses to the north of the ecliptic. The descending node is where it crosses to the south. Eclipses occur only near the lunar nodes.  The nodes also precess, like the equinoxes, but at a different speed. 
In Vedic astronomy, the two Lunar nodes were sometimes listed as invisible planets, as a convention. Sūryadeva-yajvan describes them as 'special numerical figures' created to find true motion. He also quotes Brahmagupta that the nodes were like the apogee: computational 'improvisations' . 
An older naming of the nodes was influenced by mythology. Rāhu was a mythological demon or snake that swallowed the Sun or the Moon causing eclipses.  Later on, the Vedic astronomers would understand that the eclipses occured only when the moon passed through one of it's nodes, while also in line with the Earth. Though the mythological causes of eclipses were refuted by Varāhamihira, he left the nomenclature of Rahu: The ascending lunar node he called Rahu's head, and the descending lunar node he called Rahu's tail. Later on, the nodes would be called Rāhu (ascending) and Ketu (descending). 
Eventually these names were replaced with the word Pāta.