A daydream is a visionary fantasy experienced while awake, especially one of happy, pleasant thoughts, hopes or ambitions. There are so many different types of daydreaming that there is still no consensus definition amongst psychologists.  While daydreams may include fantasies about future scenarios or plans, reminiscences about past experiences, or vivid dream-like images, they are often connected with some type of emotion.

Daydreaming may take the form of a train of thought, leading the daydreamer away from being aware of his or her immediate surroundings, and concentrating more and more on these new directions of thought. To an observer, they may appear to be affecting a blank stare into the distance, and only a sudden stimulus will startle the daydreamer out of their reverie.

While daydreaming has long been derided as a lazy, non-productive pastime, daydreaming can be constructive in some contexts. There are numerous examples of people in creative or artistic careers, such as composers, novelists and filmmakers, developing new ideas through daydreaming. Similarly, research scientists, mathematicians and physicists have developed new ideas by daydreaming about their subject areas.