**Core Concept**
Metrorrhagia refers to abnormal uterine bleeding that occurs between expected menstrual periods. It is distinct from heavy menstrual bleeding (menorrhagia) and is often linked to hormonal imbalances, polyps, or structural abnormalities in the uterus.

**Why the Correct Answer is Right**
Metrorrhagia specifically denotes bleeding that occurs outside the normal menstrual cycle, i.e., between periods. This is different from menorrhagia (heavy bleeding during periods), breakthrough bleeding (a side effect of hormonal therapy), or post-coital bleeding (caused by trauma or cervical pathology). Intermenstrual bleeding is the precise clinical definition of metrorrhagia and is a key diagnostic clue in gynecological evaluations.

**Why Each Wrong Option is Incorrect**
Option A: Heavy menstrual bleeding is defined as menorrhagia, not metrorrhagia. It refers to excessive flow during menstruation, not between periods.
Option C: Breakthrough bleeding is a specific type of bleeding seen in contraceptive use or hormone therapy, not a general term for intermenstrual bleeding.
Option D: Post-coital bleeding is due to cervical injury or lesions (e.g., cervical erosion, cancer), and is not synonymous with metrorrhagia.

**Clinical Pearl / High-Yield Fact**
Always remember: *Metrorrhagia = bleeding between periods; Menorrhagia = heavy bleeding during periods*. This distinction is critical in diagnosing underlying causes like polyps, endometriosis, or hormonal disorders.

✓ Correct Answer: B. Intermenstrual bleeding