In gradual metamorphosis, three life stages occur: egg, nymph, and adult. Insects with gradual metamorphosis are said to be hemimetabolous (hemi = part). Some entomologists refer to this type of transformation as incomplete metamorphosis.
Growth happens during the nymph stage. The nymph resembles the adult in most ways, particularly in appearance. Usually, the nymph also shares the same habitat and food as the adults, and will exhibit similar behaviors. In winged insects, the nymph develops wings externally as it molts and grows. Functional and fully-formed wings mark the adult stage.
Illustration by Debbie Hadley, using drawings from Insects - Their Ways and Means of Living by Robert Evans Snodgrass, U.S. Bureau of Entomology. These drawings are in the public domain.