What is the difference between an oocyte and a follicle?

An oocyte is a female reproductive cell that can develop into an egg. Follicles are structures in the ovaries that house and nourish oocytes as they develop. Each follicle contains a single oocyte surrounded by layers of granulosa cells and theca cells. The granulosa cells produce hormones that help the oocyte mature, while the theca cells produce hormones that help the follicle grow and develop. When an oocyte is released from its follicle, it is called ovulation.