Nocturnal (Latin: nox - night, darkness) animals are animals that are mainly active during the night. They hunt or feed during the night, and sleep during the day. Diurnal animals do it the other way around.
Scientists sometimes use the word crepuscular to describe nocturnal animals that are not active when it is very dark at night; they are mostly active near dawn, dusk, and sometimes when the moon makes a lot of light.
Many nocturnal animals have good night vision. Their large eyes may also be highly reflective when a bright light flashes them.