Final answer:
Neotony is the term that describes retaining juvenile features into adulthood.
Step-by-step explanation:
The term that describes retaining juvenile features into adulthood is neotony. Neotony is a tendency for an animal to maintain both physical and social juvenile characteristics into adulthood. This phenomenon can be observed in certain insects, such as moths and butterflies, where the final molt of the larva produces a pupa, which undergoes metamorphosis to become an adult.