The menstrual cycle is divided into two parts or phases: The phase before ovulation is called follicular phase and the phase after ovulation is called luteal phase.
The Follicular Phase: This is the part of the menstrual cycle between menstruation and ovulation. It ends at the time of ovulation. It is named "Follicular Phase" because that is the time of the growth and development of the ovarian follicles (which contain oocytes, or eggs). The follicular phase varies in length usually between 7 and 21 days.
The Luteal Phase: This is the part of the cycle that starts at ovulation and ends the day before the next menses begins. It is named after the corpus luteum, the area in the ovary after ovulation where the egg came out. The corpus luteum produces progesterone to prepare the body for pregnancy. The length of the luteal phase is usually constant around 14 days (12-16 days range).
A luteal phase defect LPD is diagnosed when the luteal phase is shorter than 12 days.