How do biologists distinguish between maximum life span, average life span, and life expectancy?

Biologists and demographers distinguish between these terms based on how they measure the duration of life within a population:

• Maximum life span: This is a theoretical value representing the longest-lived individual of a species known to date. Because it is based on the extreme limit of observed survival, it is considered a rough estimate rather than a precise biological constant.1
• Average life span: This is a statistical measure derived from analyzing mortality data across a population. It provides a more meaningful representation of typical longevity for a species than the maximum life span.1
• Life expectancy: This is a hypothetical, forward-looking estimate of the average number of years a group of individuals born at the same time can expect to live. It is calculated using life tables that project current age-specific death rates over the lifetime of that population.12

While maximum life span focuses on the outer limit of survival, life expectancy is highly sensitive to environmental factors, such as healthcare, nutrition, and local mortality rates, which can change significantly over time.23