Lucid dreaming

from answers.com

Lucid dreaming is consciously perceiving and recognizing that one is in a dream while one is sleeping, and having control over the "dreamscape", or the faux-reality dream world within a dream. Stephen LaBerge, a published author and expert on the subject, has defined it as simply realizing that one is dreaming while in a dream. Other authorities contend that in order for the state of a dreaming person to be lucid, that person must have control over his or her dreamscape (because simply having the mental idea "I am lucid" could be a creation of the subconscious itself and not a real "rational" thought). Lucid dreamers, called oneironauts, report being able to freely remember the circumstances of waking life, think cogently, and act deliberately upon reflection, all while experiencing a dreamscape that seems vividly real...read more here.