Typically, musicians will just call the descending melodic minor by the name 'natural minor.' To other musicians, like jazz musicians, 'melodic minor' simply refers to the ascending form of the melodic minor scale. This ascending/descending distinction is respected in Classical music. Why? It was felt when melodies descended the scale, it sounded better with the flatted 6th and 7th, and while melodies ascended through the scale it sounded better with the raised 6th and 7th. “Descending melodic minor” is just the plain old natural minor scale when descending. The descending melodic minor scale is another name for the natural minor scale. The ascending melodic minor scale is what I've just described-a natural minor scale with a raised 6th and 7th. There are two forms of the melodic minor scale: ascending and descending. This is a good technique to learn, and it will show up in other musical shapes on the fretboard later on. Your fingers compress and then stretch back out. If you use your first finger on the 4th degree and your fourth finger on the 5th degree of the scale, it makes shifting smoother.

B flat melodic minor descending