What is menarche?

Explanation

### Step-by-Step Solution:

1. **Understanding Menstruation**:
- Menstruation is a biological process in human females characterized by periodic bleeding. It usually occurs at an average interval of about 28 to 29 days.

2. **Defining the Menstrual Cycle**:
- The menstrual cycle is the time frame from one menstruation to the next. It involves various physiological changes in the ovaries and the uterus.

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