A cicada is an insect with large eyes wide apart on the head, and usually transparent, well-veined wings. Cicadas do not bite or sting, are benign to humans, and are not considered a pest.
Most cicadas go through a life cycle that lasts from two to five years. Some species have much longer life cycles, e.g. the Magicicada goes through a 17- or occasionally 13-year life cycle. This video is about these so called: "periodic cicadas".