What do we call an animal that is active at night?

Nocturnal - the daytime equivalent is diurnal, and the two words at dawn and dusk are crepuscular, which covers a great many animals people assume are one or the other. Rabbits, deer and most cats are crepuscular rather than nocturnal.

The mammal eye is evidence of a long night shift. For roughly a hundred million years, while dinosaurs held the daylight, mammals were small and nocturnal, and the vision we inherited shows it - most mammals have only two colour receptors, where birds and reptiles kept four. Primates later re-evolved a third, which is why we see red and green as separate colours and a dog does not.

Night vision is bought by trading detail for sensitivity. Many nocturnal animals have a mirror behind the retina, the tapetum lucidum, which bounces light back through for a second attempt and roughly doubles the sensitivity - that is the eyeshine in a torch beam. It also slightly blurs the image, which is a trade a hunting cat is happy to make and we are not.