What does "descending" mean?

Descending: Of or pertaining to descent; moving downwards. Descending constellations or signs (Astron.), those through which the planets descent toward the south. -- Descending node (Astron.), that point in a planet's orbit where it intersects the ecliptic in passing southward. -- Descending series (Math.), a series in which each term is numerically smaller than the preceding one; also, a series arranged according to descending powers of a quantity.