Douglas Harper's Etymology Dictionary
in reference to the hypothetical cloud of small objects beyond Pluto that become comets, proposed 1949 by Dutch astronomer Jan Hendrick Oort (1900-1992), and named for him by 1968.
Wikipedia
The Oort cloud ( or , named after the Dutch astronomer Jan Oort), sometimes called the Öpik–Oort cloud, is a theoretical cloud of predominantly icy planetesimals believed to surround the Sun to as far as somewhere between . It is divided into two regions: a disc-shaped inner Oort cloud (or Hills cloud) and a spherical outer Oort cloud. Both regions lie beyond the heliosphere and in interstellar space. The Kuiper belt and the scattered disc, the other two reservoirs of trans-Neptunian objects, are less than one thousandth as far from the Sun as the Oort cloud.
The outer limit of the Oort cloud defines the cosmographical boundary of the Solar System and the extent of the Sun's Hill sphere. The outer Oort cloud is only loosely bound to the Solar System, and thus is easily affected by the gravitational pull both of passing stars and of the Milky Way itself. These forces occasionally dislodge comets from their orbits within the cloud and send them toward the inner Solar System. Based on their orbits, most of the short-period comets may come from the scattered disc, but some may still have originated from the Oort cloud.
Astronomers conjecture that the matter composing the Oort cloud formed closer to the Sun and was scattered far into space by the gravitational effects of the giant planets early in the Solar System's evolution. Although no confirmed direct observations of the Oort cloud have been made, it may be the source of all long-period and Halley-type comets entering the inner Solar System, and many of the centaurs and Jupiter-family comets as well.
Usage examples of "oort cloud".
There were still plenty of stray comets at that distance, on the thin margins of the Oort Cloud.
It would then take a day to get to Mars, a week and a half to Pluto, a year to the Oort Cloud, and a few years to the nearest stars.
He was like that when we first met him, he was like that out in the Oort cloud, and he was still like that until the moment he died.
If I can persuade him to leave this place, I have to head out at once to look for Chrissie and the Tarbush in the Oort Cloud.
She was in the Oort cloud of comets, far beyond the orbit of Pluto, and she was docking on what was clearly a Heechee artifact.