This term originated in Freud’s Die Traumdeutung (“The Interpretation of Dreams”) and refers to the way in which dreams picture things from waking life that happened the very day before the dream. So, for example, if I watched The Walking Dead and dreamt that night of being attacked by zombies (as often happened when I was watching that programme), that would be day residue. Masses of empirical evidence now exists illustrating the day residue accounts for the vast majority of references to waking-life in dreams. We can dream also of our distant past, our recent past, and things anticipated for the future; but day residue seems to account for most of waking life in dreams. More recently, the dream-lag effect has been discovered.