The term over-population is best defined as the situation where

The term over-population is best defined as the situation where the population exceeds available resources. This means that the number of people in an area is greater than the resources available to sustain them, such as food, water, shelter, and health care. It can lead to various problems including poverty, environmental degradation, and a strain on infrastructure. Over-population occurs when the existing resources cannot meet the needs of the people, resulting in hardship and reduced quality of life.

In contrast, having a birth rate equal to the death rate implies a stable population over time, not necessarily over-population. Increasing birth rate and decreasing infant mortality can contribute to population growth, but they do not solely define over-population. Finally, high population density refers to a large number of people living in a small area, which could lead to over-population if resources are insufficient, but high density alone does not equate to over-population.