Plain English Meaning
A thin, wispy cloud made of ice crystals that forms very high in the sky. It looks like fine streaks or feathers and usually means good weather right now, though it can be an early sign that weather is changing.
Full Definition
A high-altitude cloud type, typically forming above 20,000 feet AGL, composed almost entirely of ice crystals and characterized by thin, wispy, fibrous, or feather-like strands. Cirrus clouds indicate fair weather at the time of observation but can signal an approaching change in weather, such as a warm front or jet stream activity.
Context Anchor
Seen in aviation weather study, weather briefings, and cloud identification when a is to recognize high cloud types.