A dream is one of the little movies in your mind that play at night, or a type of hope: you might dream of being a doctor.
Everyone dreams, and dreams tend to be weird, but the images and sounds that fill your head as you sleep are just part of the meaning of this word. People also have dreams that are kind of like plans and goals: many people dream of being movie stars. A good car runs like a dream. Something too good to be true feels like a dream. If you're acting confused, someone might say, "Stop dreaming!"