The definition of a daydream is a fantasy or series of pleasant thoughts you have when awake that helps you to escape from reality.(noun)
If you hate your job and sit in a boring meeting fantasizing about winning the lottery and walking out, this is an example of a daydream.
Daydream is defined as to imagine or fantasize.(verb)
When you imagine winning the lottery and quitting your job during a boring meeting, this is an example of when you daydream.
See daydream in Webster's New World College Dictionary
See daydream in American Heritage Dictionary 4
Learn more about daydream