to move downward, from a higher position to a lower one
The verb combines kata (down) with bainō (to go) and means simply to descend, whether by walking down a slope, traveling from an elevated city to a lower one, or stepping off a platform. It is the ordinary Greek word for downward motion and covers the full range from a man coming down from a housetop to a traveler going down from Jerusalem.
In the New Testament the word takes on a second, theologically dense dimension: divine and heavenly realities are described as descending from above. The Spirit descends on Jesus at his baptism, Jesus repeatedly identifies himself as the bread that came down from heaven, and the new Jerusalem descends from God. This usage is not metaphorical in the way a poet might speak, in John's Gospel and Revelation especially it asserts an actual movement of heavenly realities into the created order.
A smaller cluster of uses describes natural phenomena, rain, a windstorm, hailstones, coming down from the sky. These retain the plain spatial sense while portraying weather as something that originates above and falls upon the earth.