The Great Red Spot is a great high-pressure storm much like a hurricane on Earth, but it is enormous - estimated to be at least three times as large as the Earth.
It is anti-cyclonic in Jupiter's Southern hemisphere, the rotation is counterclockwise, with a period of about 6 days. The clouds associated with the Spot appear to be about 8 km above neighboring cloud tops.
There are other features similar to the Great Red Spot on the surface - like certain white spots - but none are as large as the Great Red Spot.
Presumably, the persistence of the Great Red Spot is related to the fact that it never comes over land, as in the case of a hurricane on Earth, and that it is driven by Jupiter's internal heat source.
It has been suggested that certain compounds of phosphorous are responsible for the reddish-brown hue, but this remains somewhat speculative. Thus, scientists understand the broad properties of this remarkable phenomenon, but not all the detailed features.
The Great Red Spot on Jupiter appears to be shrinking in size