1. (Science: anatomy) Generally a small sac or vesicle.
2. (Science: botany) a kind of fruit formed from a single carpel, that splits to release its seeds.
3. (Science: dermatology) a hair follicle, an invagination of the epidermis into the dermis surrounding the hair root.
4. (Science: gynaecology, physiology) An ovarian follicle, an oocyte surrounded by one or more layers of granulosa cells. As the ovarian follicle develops a cavity forms and it is then termed a graafian follicle.