A group of undifferentiated cells in an insect larva that develops into a specific adult structure. Imaginal discs are derived from the blastoderm. They do not undergo further development until the pupal stage, when they start to differentiate into adult epidermal structures, such as eyes, antennae, and wings, under the control of the hormone ecdysone. The developmental fate of the cells in each disc is determined, and different zones of the disc give rise to particular structures. For example, a fate map of the leg disc of the fruit fly Drosophila can be drawn, consisting of concentric circles of cells; the inner zones develop into the distal leg structures (tarsus and tibia), while the outermost zones give rise to the proximal structures (femur, trochanter, and coxa).