A cloud — a visible mass of condensed water vapor in the sky; commonly used in weather and descriptive contexts.
今日は雲が多くて、夕焼けがきれいだ。
There are many clouds today, and the sunset is beautiful.
雲の切れ間から山頂が顔を出した。
The mountain peak appeared through a break in the clouds.
飛行機から見る雲海はまるで絵のようだ。
The sea of clouds seen from the airplane looks like a painting.