A bat is a small flying mammal from the order Chiroptera. In nature, they have small legs, and two webbed wings. They are the only mammals who are capable of true flight, as birds are (other mammals like flying squirrels and the like actually glide).
In nature, bats range from less the 6 inches across at the wings (Kitti's hog-nosed bat) to nearly 5 foot across at the wings (Giant Golden-crowned flying-fox).
Bats are NOT rodents, despite appearances. Bats also are not blind. Large bats ("mega bats") actually have quite keen vision, while smaller bats have echlocation to guide them.