ovarian follicle

https://doi.org/10.1351/goldbook.11056

Cavity in the ovary containing a maturing ovum, at any stage of development, surrounded by its encasing cells.

Source:
PAC, 2016, 88, 713. (Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)) on page 789 [Terms] [Paper]