A stage in the life cycle of insects that do not go through complete metamorphosis (cycle of change). Most insects have four stages (1 = egg, 2 = larva, 3 = pupa, 4 = adult), but some only have three stages. This is called incomplete metamorphosis (1 = egg, 2 = nymph, 3 = adult). With incomplete metamorphosis, nymphs hatch from eggs and slowly change into adults. There is no pupa, or resting stage. Most aquatic insects have a nymph stage, since a pupa (coccoon) could not survive underwater. A few land insects, such as grasshoperrs and crickets, have a nymph stage also.

This definition is in context to Ecology. See more contextual defintions for Nymph.