the way that people do not live for ever

Her death made him more aware of his own mortality. 她的去世让他更加意识到自己终有一死。

the number of deaths within a particular society and within a particular period of time

the mortality rate 死亡率

Infant mortality is much higher in the poorest areas of the city. 在这个城市最贫困的地区，婴儿的死亡率要高得多。