Lenticular cloud
Lenticular clouds (Altocumulus lenticularis in Latin) are stationary clouds that form in the troposphere, typically in perpendicular alignment to the wind direction. They are often comparable in appearance to a lens or saucer.
There are three main types of lenticular clouds: altocumulus standing lenticular (ACSL), stratocumulus standing lenticular (SCSL), and cirrocumulus standing lenticular (CCSL), varying in altitude above the ground. Because of their unique appearance, they have been brought forward as an explanation for some unidentified flying object (UFO) sightings.