When a human female reaches a certain age,then vaginal bleeding occurs for a few days after regular intervals of time :
What does the onset of this process in human female signify ?

Explanation

**Step-by-Step Solution:**

1. **Identify the Process**: The question refers to vaginal bleeding that occurs at regular intervals in human females. This process is known as menstruation or periods.

2. **Understand the Age of Onset**: Menstruation typically begins during puberty, which occurs between the ages of 10 to 13 years.

3. **Define Menstruation**: Menstruation is a monthly cycle that lasts about 28 days, where the female body prepares for potential pregnancy. If pregnancy does not occur, the lining of the uterus sheds, resulting in vaginal bleeding.

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