Psocoptera are an order of insects that are commonly known as booklice, barklice or barkflies. They first appeared in the Permian period, 295–248 million years ago. They are often regarded as the most primitive of the hemipteroids. Their name originates from the Greek word ψῶχος, psokhos meaning gnawed or rubbed and πτερά, ptera meaning wings. There are more than 5,500 species in 41 families in three suborders. Many of these species have only been described in recent years. They range in size from 1–10 millimeters (0.04–0.4 in) in length.