Average number of years that a person born in a particular year can expect to live.

The average number of years that a person, who is born at a particular year, can expect to live is called: life expectancy.

Explanation:

This answer comes from understanding what life expectancy means, and how it is defined. Life expectancy is literally defined as the average of years, or the period, that a person is expected to live. It is also defined as the average length of time that an animal, individual, or group, are expected to live. Life expectancy depends on a various number of factors, both biological, and external to the person, that help ensure a lengthier average of life expectancy. This is also a measurement used to determine the level of development of countries, regions and the world at large.