Life expectancy at birth?

It means a person born in a certain year is expected to live up to that certain age. For example a baby born in 2008 is expected to live to be 90 years old but a person born in 1998 is expected to live to be 80 years old. That doesn't change, the person born in 1998 still has a life expectancy of 80 in the year 2008. Likewise, the baby born in 2008 will still have a life expectancy of 90 in ten or 50 years down the road.