In animals, a follicle is a small cavity in the body. One example is a hair follicle, a pit on the surface of the skin from which a hair grows. Another example is a Graafian follicle (or ovarian follicle), one of the many fluid-filled cavities in the ovaries in which an ovum (egg) develops.

In plants, a follicle is a dry single-seeded fruit that splits along one margin only to liberate the seeds (unlike a pod, which splits along both sides). Follicles occur in clusters called etaerios. They are found in plants such as larkspur, columbine, and delphiniums. See also legume.