**Core Concept**
Ovulation is a critical event in the menstrual cycle where a mature ovum (egg) is released from the ovarian follicle. This process involves a complex interplay of hormones and cellular mechanisms, ultimately leading to the rupture of the follicle and the release of the ovum into the fallopian tube.

**Why the Correct Answer is Right**
The correct answer is the result of the luteinizing hormone (LH) surge, which triggers the final stages of follicular maturation. As the follicle prepares for ovulation, it undergoes a series of changes, including the thickening of the follicular wall and the formation of a stigma (a small opening). The LH surge causes a rapid increase in the levels of progesterone and estrogen, which in turn lead to the contraction of the follicular wall and the extrusion of the ovum.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is not a relevant term in the context of ovulation.
* **Option B:** This term refers to the process of fertilization, not ovulation.
* **Option C:** This term refers to the fertilized egg, not the mature ovum released during ovulation.

**Clinical Pearl / High-Yield Fact**
The LH surge is a key trigger for ovulation, and its timing is critical for determining the fertile window in women. Understanding the hormonal mechanisms underlying ovulation is essential for fertility treatment and reproductive health.

**Correct Answer: D. Extrusion**