Crepuscular is a term use to describe animals that are primarily active during twilight, hence at dawn and at dusk. The word is derived from the Latin word crepusculum, meaning "twilight". Crepuscular is thus in contrast with diurnal and nocturnal behavior. Crepuscular animals may also be active on a bright moonlit night. Many animals that are casually described as nocturnal are in fact crepuscular. Within the definition of crepuscular are the terms matutinal (or "matinal") and vespertine, denoting species active in the dawn and dusk respectively.