A visible mass of particles of water or ice in the form of fog, mist, or haze suspended usually at a considerable height in the air is a cloud. They often appear as a light filmy, puffy, or billowy mass seeming to float in the air such as the following:
There happens to be all sorts of clouds. The names vary from such words as cirrus, stratus, cirrostratus, and altostratus. I believe the ones shown above are called cumulus.
Now cloud may also mean to become troubled, apprehensive, or distressed in appearance. Let's cloud the issue so as to make it unclear or confused. These kinds of clouds can make one confused or anxious. To cast gloom over is often the result. All sorts of names also tag these cloud as they past through our sky. For each of us, these names will vary.
Well, the clouds above have blocked the sun. They certainly appear dark and gloomy on one side. Such may be many of the days that pass before us. Yet, one can imagine where the saying "the clouds silver lining" originates. Given enough time, the cloud will pass away.