What is the definition of “life expectancy”?

The World health Organization defines “life expectancy” as the average number of years that a newborn could expect to live if he/she was to pass through life exposed to the sex-specific and age-specific death rates prevailing at the time of his/her birth for a specific year, in a given country, territory or a geographic area (https://www.who.int/data/gho/indicator-metadata-registry/imr-details/65). Life expectancy at birth reflects the overall mortality level of a population. It summarizes the mortality pattern that prevails across all age groups.