In biology, the imago is the last stage an insect attains during its metamorphosis, its process of growth and development; it also is called the imaginal stage, the stage in which the insect attains maturity. It follows the final ecdysis of the immature instars.
In a member of the Ametabola or Hemimetabola, in which metamorphosis is "incomplete", the final ecdysis follows the last immature or nymphal stage. In members of the Holometabola, in which there is a pupal stage, the final ecdysis follows emergence from the pupa, after which the metamorphosis is complete, although there is a prolonged period of maturation in some species.
The imago is the only stage during which the insect is sexually mature and, if it is a winged species, has functional wings. The imago often is referred to as the adult stage.
Members of the order Ephemeroptera (mayflies) do not have a pupal stage, but they briefly pass through an extra winged stage called the subimago. Insects at this stage have functional wings but are not yet sexually mature.
The Latin plural of imago is imagines, and this is the term generally used by entomologists – however, imagoes is also acceptable.