A dream is made up of a train of mind-pictures that form during sleep. The people and actions in these pictures seem real to the person who is dreaming.
When a person is asleep, he has little or no control over his mind. Then ideas and feelings come out to form the mind-picture known as dreams.
Dreams may be influenced (影响) by different things that are present during sleep. If a person is cold, he may dream that he is out in a snowstorm (暴风雪) .
Some people think that they do not often dream, and other people are quite sure that they do not dream at all. However, studies have shown that everyone dreams every night. If a person thinks he does not dream, it is because he does not remember dreaming when he wakes up.
As a matter of fact, not only does everyone dream, but it seems that we all need to dream. Dreams give us a chance of escape (逃离) from the rules of our real world. In dreams we can see our wishes come true. We can be rich, powerful, and successful.
The sentence "A dream is made up of a train of mind-pictures that form during sleep." means ______.